im currently helping my friend do the same. we have 2 zuki's. one beater, and another nice one. what we're going to do is use the beater as a template for what we wanna do.
from our measuring... the dual cases along with the 22RE we're using will render us with either 2-4 inches worth of extra driveshaft over the stock length of the sami's original rear shaft. we're achieving this with moving the engine forward in the frame, notching the radiator where the core support whent and running electric fans. ive looked around on pirate and seen it done. you shouldnt have any issues fitting it all in there just takes some measuring and alot of patience.
we're using a g-52 trans, the twin cases, toyota axles, 22RE, and jeep springs. we're also drilling extra holes in the spring perches in order to adjust the axles front or back 1 inch either way. hope this insight helps you out.