I had a problem initially installing engine to mate to trans, this is what I found :
The throw out fork was behind the throw out bearing, blocking the full engine - trans mating. The clutch tool was home made in my lathe! to exact tolerance.. ie perfect. This is got to be perfect.
The lite / mirror is shown at:
http://www.geocities.com/chuckw96/b80_porsche/mirror_lite.jpg
There is an access hole that the previous post pointed out at about 11 oclock from the rear of the car in the trans bell housing. When all four bolts from the engine just start to insert into the trans bell housing it is time to line up the fork into the bearing. I had to use a "proctalogist" lite and mirror, with these tools you can look through the access hole (2" dia) and move he fork from the starter hole. With the throw out bearing / fork mated the engine slid in directly.
I would strongly suggest that the access hole be used for inspection after the engine / trans is mated to verify the throw out bearing / fork mates correctly.