ive fitted an rb20det to my 66 skyline gt, now 2,300, seems a bit rich, when i paid only 1650 for mine, best bet is to shop around and get importers to out bid each other.......
secondly, ya might have trouble findin a turbo set up for your L-series Block, cause i know i did, thats why i did a complete engine.
thirdly, i am runnin the orginal diff and its holding up ok, but you should be able to get a centre out of a latter model line......
hope this helps....
Pete