As is clear from many peoples experiences, the T5, especially with upgraded internals, is good for more than the 300 bhp declared by TREMEC. If you upgrade to its successor, the TKO, it will not fit under the MkIV front bulkhead and transmission tunnel without significant modifications. Regarding, the cable clutch, if you go hydraulic, you will obviously need a different pedal actuation, which by the sound of it, our friend Wescott has already solved.
I’ve prepared and extensive pictorial account of the 18 months of work involved in transforming my MkIV to 427 FE. If any Mk IV owner is interested in reading it and are an ACOC number, PM me with your membership and chassis no and I will email you a copy. Please also state that you undertake not to republish the material.