Hay mate, i think its a great idea. I found the nissan article were the rb25 block uses 20 crank and sohc head and carby lol.
Im a big fan of the 20 and only dont like the 25 because of its slow revving nature without hi rpm compared to the 20, revs isnt everything but its fun an sounds good lol.
If you find out anymore about what bearings, rings,pistons sizes etc throw us a pm as im interested in doing the same thing sometime.
Stupid question, but does a lower compression turbo'd car help make it rev quicker ?
Good luck with it all.