Seem to be at least two types.

[kresty]

According to wookiepeedia, their names are LIN-V8K and LIN-V8M.  V8K is the one the Jawas were trying to pawn off on the Lars, and V8M was apparently seen on the Death Star (though I didn't try to find the frame).

LIN-V8M
Apparently on Death Star, not sure where/when (ANH)

LIN-V8K
LIN-V8K

I'm not even sure if these are close to the same scale though.  The V8M Death Star one clearly has some significant differences.  It's been weathered a lot, much of the black is missing.  The tracks look very different to me as well.  It's hard to tell because the photo's so small, but the V8M Death Star version looks more aggressive to me, and not the same spacing as the Treadwell-like tracks on the Jawa -V8K version.  

I suppose the track differences I wonder about could just be the camera angles and stuff, and obviously the paint/weathering could've just been redecoration of the same model.