Looking for some info, I run Poston Long tube headers on my 71 455 Skylark. Has anyone had any clearance issues with these headers doing a manual to 4speed swap?
Not sure about poston but MT headers are doable had to make trans mount, shouldn't be an issue there with the postons, but you may have to reposition the return spring as I had to
If memory serves the Poston hedders never fit with a 4 spd. TA and Hooker made sure that it would fit.
Before I restored my '70 GS I had a 455 in it with a 4 speed and Poston headers with no issues. If you already have them I would try them. Ken