The largest displacement you could stuff into an 88 chassis (without serious work) is the B20B or B20Z... the DOHC Honda CRV engines, however if the cash is availible the B18C Integra GS-R is (IMHO) the only way to go, with a nice Skunk2 intake manifold to get rid of the GS-R variable-length butterly plate whatever its called intake manifold. If money is an issue, the B18A/B from 90+ Integras should have more spunk in the civic body then the integra, based purely on weight... that is, if you can survive without VTEC.

BTW, why you selling your RX-7? Too many electrical issues? I know mine honestly has at least 15. It's amazing it still runs.