been reading some old magazine ( 1975 PCA) that a good friend of mine gave me and i found this:
porsche dealer were already toying with bigger engine in 75
here is the text: they say that the 901 casing is weak so here is it:

to transmit torque from a big engine a high capacity clutch is needed, the clutch is redily available ( 2.7 carrera) but the release action is is just the opposite of the 914. however this is a super blessing in disguise as ,, by installing the 914 gear in a 911 (70-71) case the clutch action is reverse, this permit the 914 cable pulley affair to be completely discarted and replaced by a strait pull clutch cable and if you use the 72 911 cable it will fit like it was original,,

this might be a better route than the other that are done now

have fun

The 911 case and the 901 case are virtually the same. The advantage is only in the clutch. The big change was in 1972 with the advent of the 915 transmission, and the much stonger gearset.

this is used by quite a few racers..
roger sheridan's used tranny that may still be for sale has this....

it gives you better clutch, but doesn't solve the problems that having complete transmission of big power then creates in a 901 box...

I don't think the clutch is the weak link in the 901 really.

brant