Ah, so there is a benefit of having an RBM tower...
I _YET_ do not have my ppc/g-rex, but I did borrow a friends ppc/grex to see if it fits inside, and it fitted very well!
The difference of RBM case, is that the ZORROII/ACCELERATOR bus are not on top of the a1200 m/b, but they are back-to-back, facing opposite to each other...