Or you could chip the PR4 and make it Vtec... or you could use a chipped PM6, or you could use the PS9 chipped and use the auto lockup solenoid (A8) for the Vtec solenoid... using the stock maps and only editing that one thing, then throwing some better maps at your topend (after crossover).
In short, you actually have a few options for OBD-0... use whatever one is best for you... probably the PR3 if you can get one readily.