For future reference, it's better to just start a new thread than bring back one from a year ago.
Anyway, there isn't really an "OBD1A", it's just OBD1. So you'll need a conversion harness that goes from OBD2A to OBD1. And I hope you know that the Civic's transmission won't bolt up to the B18. You'll need a B-series transmission as well.
Since you need a new tranny anyway, this would be a good opportunity to convert to manual, if that's something that interests you. I would encourage it actually, because the LS auto transmission is an absolute turd.
If you insist on keeping it automatic though, then you'll need to to let whoever makes your conversion harness know that they're working with an auto tranny.
Good luck.