I have a set of DC Sports 4-2-1 Headers that came with my car that the kid claims are specifically for a "ZC". I don't know much about D-series motors and stuff but I don't see why these wouldn't just work with all D series motors.

Even if they have larger runners, the overlap would be on the Header side not the engine side so it woldnt matter as long as you got a good gasket right?

 

Unless the kid did it himself, he's just parroting what he's been told. Or maybe trying to hype what he was selling.

The OEM ZC header was 4-2-1 and the a6 was 4-1

AFAIK DC never made a ZC specific header. People had a couple options...
1. buying the a6 header and just bolting it on. Not the best solution but it works.
2. buying the a6 header and port matching. The bolt pattern between the two is identical but the actual exhaust ports are off about 1/16". Grind a little off the header side and they fit perfect.
3. mix and match from the DC sports parts. Some people have managed to get primaries for an 88-89 integra and mate it to an a6 downpipe. Hard to find just half a header though.