Steve, this is off subject but your 66 sounds almost identical to mine!! Which is still being assembled. What caught my attention was the 781 heads. I have the posi, the 3:73, and 781's. I purposely sought the 781's to put on my 396 tho! Better flow, runners and open chambers. I have to finish the block yet by installing high dome pistons and new cam and bearings. I'm hoping I made the right choice with those 781's, I know its a little different but I'm willing to try. Did you have any problems with headers or did you keep the 454 exhaust manifolds? I never inquired about fitment issues cuz I thought the exhaust ports would all be the same. Am I right? Thanks