I found your answer (below) to a similar problem I am having in trying to mate my 915 transmission to the 2.7 motor ('77 911S). I'm not sure what the release shaft is, but moving the shaft that controls the throw out arm doesn't appear to affect alignment. The transmission stops about an inch short of mating to the motor. I used the clutch alignment tool when attaching the new clutch. Can you offer an ideas of what might be causing this problem?
> if it's a 915 trans, you have to eyeball the t/o bearing and fork with a mirror and flashlight thru the hole in the top of the bellhousing, so they engage as the units are pushed together. turning the release shaft underneath lines them up for mating.