Running modified (Nosram 4.5T octa), with new diff cups (Tamiya diff v2) and new spec-r 3mm blades for Tamiya, broken in two runs. Yes TWO runs (5-6 minutes run) and diff cups wear.
With 3.5mm Associated TC-6 blades, there is no trouble, but is necessary some work (little work). You can take worn diff cups to make it of 3.5mm.
I have Spec-r 3.5mm blades for Yokomo still not tested, that fits good and maybe work.
Diff with poor "machined" recycled cups:
Associated TC-6 blades in tamiya shaft after 10 runs (rear):
Now you can see how it fits:
Today, after 20 runs, still works. Now you can see that a poor mod with damaged diff cups runs good. Actually I'm running with stock front pulley and alu shafts rear (with 3.5mm tc-6 blades)