The 280ZX does not have a programmed PROM, it is completely analog. It is a BOSCHE system, same as used on Alfa Romeo and others. There are ways to fool the system using series or parallel resistors or potentiometers. Try to find a GOOD book about the BOSCHE system, that may unlock some secrets of tuning the 280Z/ZX computer. The 280Z and 280ZX FI systems are basically the same, but in 1981 the O2 sensor feedback was added; there is also an additional connector on the ignition module on the distributor on the later cars.
Jim Wold Technology has a reworked 300ZX (digital) ECU that works on 280ZX, check it out (but I bet it will be expensive),
> Does anyone have the computer code to the
> ECU for 81 to 83 ZX or ZXT. I Mean the
> Actual program that controls the ECU. Any
> input is welcomed