Hi,
I put a 1986 930 4 speed long bell housing in my 1975 911 with a V8 things needed to do are ..
modify front trans mount .. so trans fits more forward about 1.5 "
disassemble trans and cut bell housing and pinion shaft down about 1.3 inches, and machine a new centering grove in bell housing
get a 930 petal assy .. you need the clutch petal and arm as the 930 petal arm is longer than a 915 arm so when you depress clutch petal you get more throw.
If you go with a early short version of the 930 .. you dont have to cut the trans box, but then again the later boxes are stronger and 10 years newer .. thats why i went with a late long bell housing 930
here is a picture..
Take care - Joe -