Hey Trevor,
You have two possible ways to deal with this issue at the rear. First one is a bit tacky but workable. Second one makes for a clean installation.
* place 2mm shims between the two side plates and the lower chassis plate; plus a shim on the center pivot post
* replace the two side plates (motor side & left side) with the ones intended for taller tires (as used on the F1 kit). These are part numbers 3440 and 3440.
I used the second one myself to convert my WGT SE over to a WGT-R (rubber) chassis. WGT-R has 60mm high tires.
Cheers!
Bill