Here’s the last thing you can check for now.
like stated. If there is a 1-5-4 cam in the car, the injector wiring would need to have been changed to fire at the right time. It’s either cut and spliced out at the car, or repinned at the ECU.
not sure how good you are at elevtrical troubleshooting, but you can pull the computer connector and look at the pins and see if the wire colors match up.
for example, injector 3 is the Brown wire with yellow stripe, and should be in pin 12 on the ECU. Injector 5 is tan with light blue stripe and in pin 14. If those are swapped, that’s a big clue.
If not, then you might want to test continuity from the wire at the ECU. One wire should do it. Test injector 3. Easy way to do it to prob pin 12 on the ECU connector to the brown/tab wire on injector 3. You might need a piece of wire if your meter won’t reach. If it rings out, the injector order is wired the right way for a 1-3-7 firing order.
that should be plenty to keep you busy. Let us know what is in your scope of ability to do and not able to do.
also, pictures of MAF part number as well as the throttle body and general wiring pics woukd help spot something out of place.