The oppliger kit is Mt75 4x4, you might be lucky as he is working on close ratio 6 speed and I expect that would still have Same top speed as standard.

Supra diff is not hard, I used a 6 degree beam from MK and the beam was adapted to take a supra diff with MK cover and MK bladed adjustable Anti Roll Bar. I have the weir spring kit. The front is the weak point so you may need to consider options such as r n d. Bara motorsport can help advise.