Used headers? Look for warped flanges that were from overtorquing the header bolts. Excessive rust and cracked welds too.

Personally, TTI's and Doug's are, I'm sure, very nice but I can live with Hookers. I got the 1&7/8" B/RB headers for my 69 Rr, sent them in for ceramic coating, they look great. Hedman makes a decent product too. The trouble with used is the varying opinions on what is "a little rust".

The top-of-the-line headers have 3/8" flanges. I like 16 gauge tubing, race headers are 18 gauge. For a mild-to-tepid 383, 1&3/4" tubing headers will perform great. If you want street/strip or strip only go with the 1&7/8" at a minimum.