Air and Exhaust Question?

High idle as you describe, with a stock cam (IE the cam is not screwing with the carb metering)

is most likely one or a combo of
1--Vacuum leak. Use a combo of stuff to find. Use a length of fuel hose to your ear and probe around the base of the carb. Use a water spray bottle to "spritz" a fine mist of spray here and there at the carb base, which will change the idle if you find the leak. Don't forget to examine carefully any/ all vacuum hoses such as the PCV valve and brake booster if used. Plug them off, inspect, etc

2--Interference with the carb/ mount. Could be a combo of wrong base gasket interfering with throttle blades, linkage hitting the manifold casting and not allowing full return or even something bent/ etc with the carb linkage itself, AND..............

the throttle cable or kickdown linkage may not be properly adjusted in order to allow the throttle to fully close


So far as your "buildup," I'm REALLY happy with a mid--70's smog engine I bought off Craigslist in my 67.

70'ss turned out to be low miles smoggy engine, 200 bucks

Installed approximate equivalent of a 340 "stick" cam. Do NOT go "too big" on the cam when you get one

Cheap Hedman headers, which I won't buy again. Poor fit, no excuse

Torquelflite, as I can't row a clutch/ 4 speed anymore. I found a reverse pattern, manual valve body, "so it's still fun," LOL

3.7x rear gear and fairly tall tires gives me about 3200 at 70

600 -ish cfm carb worked great, but in my case went with Edelbrock injection I bought used. The threads:

http://www.forabodiesonly.com/mopar/showthread.php?t=205959&highlight=pro-jection

http://www.forabodiesonly.com/mopar/showthread.php?p=1969670768#post1969670768

And no, you certainly don't need a new cam to run headers, but the headers might be overkill without it. If you already have dual exhaust, I'd put a cam in first. If not, go ahead with headers first.