I have a 1999 SVTC with a return type fuel rail and a wiring harness and XGT2 PCM both from a 2000 returnless SVTC. The car runs great, but I get a P0193 code for a high input from the Fuel Pressure Sensor. The problem is the return type system does not have a FPS and the PCM is always looking for it. With the CEL it will not pass the stinkin emissions here in the ATL metro. No emissions, no plate, no drivey. Its a load of crap.
I have tried to create a MIL Eliminator to trick the PCM into thinking the FPS is there, and it clears the P0193 code, but now I have a P0172 and P0175, System too Rich Bank 1 and 2. I also tried a 1999 Return Type PCM, SFG0, and it did not work at all. There has to be a fix to this.
Good luck with it. Wiring harnesses are hard to find. If you have someone willing to try to mod a wiring harness, they probably know what to do.