Shorty headers for 360 in A body

Are you sure you're talking about the same headers? They have .310" which is basically 5/16". That ain't the monstrous 3/8" some are, but it's pretty thick. I have a friend who has a big block set on a C body wagon and they're pretty nice.

Yes headman’s.

He drives the car regularly. I think had 20-30K miles on headers. They just had all kinds of quality issues.

The threads here are similar and they take time modifying to fit.