Frank, SDS makes a piggyback fuel computer that will drive 2-4 extra injectors, programmable. It leaves the stock ecu alone. Your FPR won't work with it, I think. It wants just a MAP referenced constant fuel pressure. All it needs is rpm, tps, and your programming, plus 2-4 injectors and a fuel feed/return for them, and two weld on injector bungs. SDS also has nifty injector bungs with injector retainers so you don't need to fab a fuel rail, but the fuel line needs to be attached to the injectors with clamps.

You've hit the demon I was afraid you'd run up on - detonation due to lean out plus 8.9:1 compression.