Hallo
If you have the old 912 E engine you can swap over nearly all parts but you will find the bus has a other oilfillerlocation and you have to run zhat trough the shroud. If you have a Later bus engine like CJ you have additinal other exoust ports so the 912 excangers will not match ( early are oval late are retangualr ).
Also the 912/914 2,0 heads are special for those cars and have a relocatet spark pkug position. If you use normal heads you have to relocate the holes on the original coooling shroud.
Best would be to swap the P&C with the heads over to the bus engine and then rebuild the original short block for a later reswap
( or offer the block to garry kutter on the 914 board
http://forums.pelicanparts.com/porsche-914-914-6-technical-forum/70758-hole-engine-case-post468624.html )
Grüsse