The 901 can be primarily found in the 914 though some early 911's had them as well.
I believe the reason the 73-74 was more highly regarded was due to the change in shifting linkage/mechanism. That fact doesn't really matter due to the nosecone being changed to allow it to be used in a rear engine application.
Virtually any engine can be mated to these transmissions. Kennedy Engineered Products can mate virtually anything to these
http://www.kennedyeng.com/. But to mount a T1, TIV or WBX doesn't require anything more than the right combination of clutch, pressure plate and flywheel.
Browse the transmission section here and you'll be amazed at what you find.
Bugat5speed here in the US and Germany have been exceptionally helpful in supplying mounting options for us to be able to install these with minimal 'sex-change operation' antics.
Good luck!