901's come in '66 to '69 911 and 912 Porsche's. They can sell for $200-$800 depending on condition. Look in the Tech article section and links for info on installing one. Type 4s in 914s used a variation of the 901 so the clutch/flywheel will bolt right up and work fine in a regular 901. A 4 speed shifter will work OK. How long will it take? That's up to you, could be a day or a week, depending on your skills in fabrication of the mounts and linkage.
Again, read the tech articles and old posts. Also visit the ShopTalkForums (STF) at
www.shoptalkforums.com then go to the eurolook forum. Most of us here also visit there, those forums have been around for a couple of years. Lots of good info on this subject in the old posts. I prefer these new GL forums but still go to STF to see if anythin new comes up (rarely these days).
ken