I suspect that used headers don't come up too often. As for if they'll fit Gen1 & Gen2 I suspect they should, as Gen1 guys are installing the 1998+ tubular factory headers (as opposed to cast iron manifolds - yipee!) on their Gen1 cars (probably why headers are giving the most HP gains on the Gen1 cars).
Also I'm not too sure I'd buy a used cam or roller rockers, I don't think the cost savings outweights the potential failure risk.
Cal