Moving the engine back

You still need to do some homework for the exsiting center of gravity. Once you have the 4 wheel scales this site has a calculator for it...

http://robrobinette.com/cg_height_calc.htm

The lighter the car, the greater the affect. So a back half A body I'd figure will run close to 3K w/driver, maybe more depending. So I'd think 6" will make a decent difference. Whether it's enough to make it all worth while - that's another story...lol.