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The history of Tamiya monster trucks is interesting. They are one of the only companies to have made scale monster trucks that actually look and perform like the real thing instead of just calling any stunt truck with big tires a monster truck. It started with the 58065 Clod Buster way back in 1987 which used solid axles, 4WD, and 4WS, just the right formula for a monster truck. The 58232 Juggernaut followed in 1999 using the same size (but different tread) giant tires but new axles and much stronger metal chassis plates. The 58280 TXT-1 (Tamiya Extreme Truck) came out only 2 years later in 2001 following much the same formula. It reverted to the original Clod tires and refined the Juggernaut with lighter chassis plates and a cantilever suspension. All of these were truly huge trucks. The Rock Buster is the first model to use the TLT-1 (Tamiya Little Truck) chassis, and it a mini TXT-1 in virtually every way. It has metal side plates, cantilever suspension, solid axles, 4WS, and even the same paint scheme as the TXT-1. The difference is the tiny 1:18 scale size.

I really had no idea what to expect from this model. I'd been told it didn't sell very well. That might partly be because of the scale, but it could also be because of the 3 open differentials and low ground clearance which combine to make it nearly useless off road. It could also be because of the requirement to use an oddly sized battery pack. This was rectified with the 47202 Rock Climber, the only other model to ever use the TLT-1 chassis, which I understand sold even worse. I actually would have preferred the Rock Climber based strictly on appearance, but I was never able to find one available for sale.

I actually really like the scale of this truck. With the tiny size combined with a 540 motor, it has all the power you could possibly ask for at a low price. It is small enough to drive indoors but big enough to handle grass and gravel with no problem at all. It is as sturdy as a tank and looks good. Of course it can't compete with a true crawler off road, can't compete with a CC-01 for scale detail, and can't compete with a touring car for performance. But I dont' think it was intended to do any of those things. It was intended to be a scale accurate, but tiny, monster truck. It managed that admirably.

I haven't made any modifications at all to this chassis, a rarity for me. I actually quite like the way it performs as is.

This model comes in a different type of box that I've seen on a Tamiya model before. It is small, square, and stands upright with a handle at the top. Looking inside, the body is much smaller than I was anticipating even though I knew this was a 1/18 scale model. There is no fancy packaging inside, but the cardboard insert is important. The box can be used as a carrying case for the completed model and the insert serves as a support so the model stays centered.
Much about this model is not what you would expect. In general, you'd expect a 4WD truck to have a transfer case but no center differential. In this case, there is a center ball diff. If that weren't unusual enough, the connection between the spur gear shaft and the differential shaft is a drive belt. There is no slipper clutch, but theoretically the belt would break before any gears. Nothing is likely to ever break though. With 3 open differentials you lose all torque if any on wheel comes off the ground.
The completed gearbox. This is a very tall layout with almost no access once the chassis is assembled. Belt maintenance requires a complete teardown.
The vertical aluminum chassis side plates are ridiculous. The bending moment of inertia is enormous which means this thing is not going to bend or twist. This structure would be plenty adequate for a 1/8 scale model; at 1/18 it is built like a tank. The gearbox sits between the plates. In the second image you can see the cranks for the cantilever suspension. You can also see the unusually shaped battery tray by the straps which will not allow use of a standard 6cell NiMH pack.

The metal differentials in this truck are clearly meant for 1:10 scale models (or even bigger). There are some advantages to this: they will never break in this application and the axles could be used in larger trucks. The disadvantage is that the pumpkin is really big which results in very little ground clearance. I installed ball bearings throughout as part of my original build.
The front and rear axles are identical if you build them with the four wheel steering option. You can also build the rear axle with locked steering. This is a servo-on-axle system with a nice high torque servo saver on each.
These are some surprisingly nice shocks. They feature an anodized aluminum housing and a very long stroke. The diameter is small which means there isn't much oil volume, but this truck also weighs very little. In the left hand image you can see how the shock bodies came out of the box. The o-rings and c-clips in the rod end are pre-installed, probably because most people won't have a c-clip pliers this small. The head end threads off for filling.
Now the axles are installed into the chassis. Both front and rear use identical 4-link assemblies and drive shafts. Because of the cantilever suspension, there is an additonal set of vertical links which connect to axle to the shock crank. Between this and the steering, this makes for a lot of link building
This is how the completed chassis fits into the storage and carrying box. The center cardboard support surrounds the chassis rails and sits on the axles. It works very well to protect the model.

Because the TLT-1 Rock Buster is a miniature version of the TXT-1, it was important to me to follow the box art and maintain the look. Although it looks like it would be very complicated to mask and paint the delineation between yellow and blue, it was actually very simple. Only the nose is painted yellow; the rest is stickers. This also means it is very important that you use the right yellow or the stickers won't match. I think the body came out perfectly. Note that it does not have clear windows which means they don't need to be masked. Instead they are just stickers.

TLT are real fun little trucks, I've owned 2 of them and both got modded out of the box.
I got both versions, and have the same box as you have.

Axles were common to be used in custom rigs, I have built 6 or 7 rigs so far with them, and think at the moment I got about the same numbers of axle housings for future projects.
The diffs are the same as the ones fitted to the semi trucks, actually the TLT axles are based on the semi axles.
Diffs are also used in the Hi-Lift series, with the Hilux variant being lockable.
Most times I use hot glue to lock the diffs, since it's easy to remove if needed.

The center balldiff is TA04 if I'm not mistaken.
Axles also use TA04 uprights

For future ref so are the Hi-Lift axles 3mm wider each side than the TLT ones, except the driveshafts and the lockable diffhousing and the pumpkin design, they are the same.

TLT axle parts are getting harder to come by now, but the if you need better gears, there is a HD variant for the listed for the semi trucks, but they are exactly the same as the TLT design.
RC4WD also made some parts that are intended for their stuff, but fit TLT ad well, I'm just blank in my head right now.

Thanks for all the extra information. I knew I had seen that diff before but couldn't remember where. Must have been in my King Hauler. I've also built the F-350 high lift.

Impressive little truck. And interesting.