From what I've seen the N/A tranny can handle about 250. I know a guy local here in Gainesville that is running a 13b-re on a n/a tranny in a FC. But he still has stock twins, stock boost, stock everything. Their is no point in making a custom drive shaft. Most deals online come with the turbo tranny. Just source a rear end with half shafts and your good to go for drive line wise. Oh and also you want to make sure the model your starting with is already a 5 lug. That will make life easier. If not then you got to convert everything from 4 to 5 lug.

Here is a good write-up from rx7club. Also 99.9% of your answer can be found on rx7club.com

My NA to Tii JDM Swap!!! - RX-7 Owners Club