I am in the process of putting a new or different 350 in my car. It is a 4-bolt 350 with a one piece rear seal. I found out today that I had to have a different flex-plate, an externally balanced one, I had a two piece seal motor before. The big question is will the balancer that was on my old motor work?? I know that there are internally balanced balancers and external ones, the one that I have is a stock 6 3/4 balancer and is just fine so I hope that I don't have to get another one!!!!! If there is someone out there that knows what the deal is please let me know, I don't want to mess up a new motor!!!!! Thanks NORT

 

the balancers interchange, just the flexplates don't.

 

The harmonic damper you describe is from a 305. 305's & 350's are internally ballanced. The damper will work the flexplate / flywheel will not. I would reccomend getting a 350 8in damper so you can use the 3 O-clock timing position. The hardest part with using a 6in is finding where the timing tab should be located.