I just got a van with the 99 5.7L motor but it came with the 4L80 trans. I have the TH350 in my car and the only problem i have right now is the flywheel. Can i use the fly wheel from my old 79 350 or is it different, if not what flywheel do i need?

 

No, you can't use the '79 flexplate. As to which one you need, it has to match the starter. If your '79 engine has been using a 153-tooth flexplate, then the flexplate for any '87-'92 V8 F-car will work. But you probably will find both engines originally came with 168-tooth flexplates. If so, the one from the donor van should work.