Thats a bit crappy. The shit will hit the fane when whoever your friend sold the engine to's engine blows up and they find it has standard gear in there...
Power FC's are find, tested and proven on so many cars its not funny. As far as the Profec B's are concerned, i've used one on all of my cars and have had not one problem with them (except one which just made an annoying tick).
I had an S15 and now i have my GTR. The S15 was a very good car and very comfortable to drive.
Import one if you can they come out a heap cheaper than buying one here.
There are many threads talking about rebuilds. Best thing to do is probably talk to DirtGarage. Check out NYTSKY (sorry if spelt it wrong) thread on his engine rebuild.
Bloke the silviawa forums dropped a vh45de into a s13. Have a look on those forums about it. I do remember though he had to cut a hole in the bonnet because the engine is pretty high.