Just my humble opinion but an FD with an LS1/7 is a much better swap than 2JZ-GTE. From what I have read the V8 RX-7 is actually lighter than the 13B original on account of the aluminum engine block.
My guess is the suspension dynamics are better also with the V8 than 2JZ.
Check it out:
http://www.hinsonsupercars.com/