I have a B20B in my '99 Civic... I'm looking to replace my B18B-LS manifold. I'm looking for a header that will allow me to run the Cat ('97 Integra LS) because I need to stay Emissions complaint in MD.

The LS manifold and cat are unmodified.

 

So find another LS header with the same length

 

Get whatever header you want, buy universal cat converter, have muffler weld on flange. Bolt up to your exhaust. Done.