So I was looking around on rockauto, and I noticed an oem-ish exhaust the claimed to be for an automatic Integra only. Just wondering what the difference could be.

 

Nothing.

The only exhaust difference is the extension piece that a 4 door has.

 

90-91 and 92-93 header/cat/exhausts are also slightly different in length . Most aftermarket exhausts will require an extension piece to be used on 92-93. I'd be more worried about the model and year differences than auto vs manual transmission difference.

 

catback wise they're the same it's the exhaust manifold that see's the difference and the CAT.

 

No, you're wrong.

"The 90-91 header is longer than the 92-93 header, the 90-91 cat is shorter than the 92-93 cat, and the 90-91 exhaust is shorter than the 92-93 exhaust. This means that if put a 92-93 header on your 90-91 teg simply getting a 92-93 exhaust will not make up the full length, you would also need a 92-93 cat." -Colin

G2IC - Catalytic Converter Length. 90-91 vs 92-93