Input shaft isn't a problem for fitting the MTX-75, but there are a bunch of other issues (not problems per se) that caused me to RUN (not walk) away from the MTX-75 install I was attempting, I already owned the tranny and a Torsen LSD and sold both pieces at a loss to get away from it....
I'd go for the MTX IV over the MTX-75, and I wouldn't go for the MTX IV over my Mazda combo... At least if I shred my tranny it is new stuff and parts and spare trannys abound. Wish that were the case for the MTX IV.
See MTX-75 hurdles here:
http://www.shoforum.com/showthread.php?t=52955