Renix to OBD-II: You have to replace ALL the renix sensors, TB, add a after-cat O-2 sensor, the wiring harness, (inside and out) computer, gas tank and pump, TCU, evap system, and I've probably left out a few things. Really not worth it.
The renix system isn't "bad". The difference between 1st year renix and last year OD-II "HO" is 19hp: 177 to 196. Most of the HP improvement was due to mechanical improvements, not electronics. The electronic upgrades were due to govt mandates and/or emissions.
If you're already running a late model cam('96 was an HO, right?)and you have the '98 head, you already have most of the mechanical improvements. Try getting a late model(HO) intake, or the '99-up intake, a good header, late model TB converted for the renix sensors, modern multi-port injectors, and if you want to get really crazy, a aftermarket "RV grind" cam. That'll bump you a little over 200hp, and be a LOT easier then converting to either OBD system.
Edit: Oops! read that wrong: 'thought you said "98 head" not "88 head". Add a late model head to the list: up to '99, don NOT get a '00-01 head, especially out of a junk yard or "re-manufactured". Still easier then the electronic conversion.