It doesn't affect the weight distribution significantly. Check www.torquecentral.com for the V8 RX-7 forum, which is the best info resource. Check www.hinsonsupercars.com for the best mount kit/accessories for the swap. The best setup is probably to buy the Hinson subframe and a few other of their hard parts, then put the rest of it (cooling system, driveshaft, wiring job, headers/exhaust/intake, fuel system) together yourself with less expensive parts.

This is a swap I am seriously considering as my next project. I've decided on using an LS1 but I'm still not sure on the car to put it in. The FD is probably the sexiest, but you can also put it in an FC, an SA/FB, all of the Z cars Z32, Z31, 280Z, 260Z, 240Z, and now even in an S14 240SX with a mount kit for the S13 coming soon. My favorites are the S14, the FD, and the FC. The new Z cars are too heavy and the old ones are too... well, too old.