TTi step vs. 340 manifolds

Header will gain across the power band and better sound too. TTI and Dougs fit well, hang up tight, don't leak ect unlike some of the low grade junk out there.

If you are die hard stock appearing you could swap to the earlier high flow passengers side manifold remove heat riser, install a non-pinched driver's side head pipe, straight through mufflers such as Dynomax Ultra Flow, and reproduction exhaust tips that don't have that super small inner diameter choking it down. Mandrel bent pipes front to back will also improve flow. So there are significant gains to be had without swapping to headers and maintaining stock appearance.

And if you swap to headers and you have stock exhaust tips if they are anything like what was on my '69 they choke like 1 1/2" inner diameter which is not going to flow what so ever.