Exh manifolds in an Early A...

Use what manifolds you have on hand. Spend spare hours with a carbide bit and
enlarge and match up the ports and the outlet as deep as you can. Dyno test was
written on SBM manifolds and the differences in output did not amount to a dime. People
still chasing 340 manifolds as a myth for big bucks. If you after very high RPMs
its different then just get headers.