a rev limitter can be less soft, most OEMs (at least in that era) used fuel cut to rev limit. that's partly why MSD has a selling point in their offering.

it's "Hondata" and with a stock PM6 ECU I doubt you have anything of theirs. you seem to have this one figured out.

you do "need" a 4-wire O2 sensor and OBD1 style distributor to run a hondata S200 or S300. I'd recommend a plug and play ECU like MSPNP2 from DIYAutotune, or get someone to build you a DIYPNP, either of which you can use along with a OBD0 to OBD1 harness adapter but keeping the OBD0 distributor. I think AEM still offers their PnP solution to the CRX, too. and Zdyne makes a decent update for the PM6, too. higher end stuff like MS2, haltech, Motec, etc... are legal and can all be adapted to the OEM harness or a custom harness can be made.

it might also be possible to transplant the guts of an OBD1 distributor into an OBD0 housing. I never tried. the wiring and pickups are all there, the important differences are the shape of the case, connector, and the number of teeth on the wheel.