I've tried several combinations.
standard chassis + 2.5mm top deck and standard
are not ideal for carpet running...maybe med to high asphalt but not sure..
The yok hard chassis + 2.5mm
will work for low to med bite carpet on rubber tires only.
the best combo for me so far for high grip track w foam tires =
the yok hard chassis+ 3mm top deck but even that was not totally effective, still needed that little something.
That's why a lot carpet runners are looking for the ever elusive 3 or 3.5 bottom deck with milled pockets...
You're correct about the diff parts...front and rear are identical. get those Yok ceramic diff balls they work wonders.
...i've had diffs last me about 2 1/2 without needed a rebuild.