Header Size Recommendation

Without doubt, 1-3/4 primary tube, 3 inch collector, 3 inch exhaust for the track, 2-1/2 for street.
(Quiter, that's all. If you care for such things of course.)
QUALITY muffler!

This leaves you with Hooker Super Comps or TTI headers. I am unsure if Hedman makes 1-3/4 headers for A bodies. But look into there "Hustler" line.

Header length will be decided for you by the manufacturer. No choice unless your nutty enough to use shorty headers.