I'm going to look at a 70 455
What ever you find looking at the timing chain would be ideal. lol
Q-jet 800 cfm is able to satisfy the BB.
I had messed with several different 800 qjets on my 455. Just couldnt get any of them to run better than the ole 750 qjet Ive ran since the early 90s. My 455 does make 425-450 hp and gets 20 mpgs. Ill have long excepted my failure. ha
Imo for a stock ish 455 swap use the w z A-body 442 manifolds.
With some decent compression, cam and head flow iron exhaust manifolds can make some ok power. Up to 2005 iirc I was anti headers. My 84 with x/y manifolds ran best 12.5 in heat. Way back when I found a set of unused Abody sbo headers in the back seat of a car at the local junkyard. Had them in the corner of my garage for like 4-5yrs until I decided to make them fit. It was abit daunting task at first, I realized I couldnt make full lengths so they became shorty or mid length or whatever someone would call them. For being my first set and they turned out pretty sweet. With no other changes my car went to best 12.0 in the quarter. From being anti header I have modified 5 sets of headers to fit my car all in different configurations. I have sets 6-7-8 waiting for some ambition.