My first Mopar. 67 Barracuda

Fenderwell headers are horrid! (hope you don't like your front tires too much) Problem with mounting regular headers, there is little to no room!! Unless you can find or build a set of custom headers, good luck. Hell even headers on a SB don't fit that well.
The passenger side headers usually go in pretty decent but the drivers side, You'll run into the same issues as your Big block. Big blocks don't fit well at all in those little A bodies. Another thing, big block A bodies don't handle well in turns but for all out straight runs,.... <evil grin>
Looks like you're having fun with it though. I know I will when I get around to my 67 Fishy! ;)