65 dart 318 swap- manifolds?

That should make no difference at all. That is what I would do If I were you. Unless you want to get some headers. By the way, I'm going to be doing a 360/904 swap in my '65 barracuda. So lets keep in touch. I'd like to hear any issues that you come up against. Thanks. And WELCOME!!!!!! You should stick around on here. You will meet the best people in the world on this site. I've become addicted to being a part of this wonderful site. Oh, did you change out the steering center link??? That is something that you have to do to put a V8 into your car. It actually sounds like that may be your problem. Check under your car. Look at the link under your oil pan. Is your pan hitting it?? I'll bet that is what is going on here. You must change out the slant 6 center link for the V8 center link. You dont have to change the K-member though.