I have 87 mustang gt that i have made a MAF car, my question is, is the A9L computer a plug and play or do I need to have it programed to the engine set up that I have, such as 70mm MAF, 76mm thottle body F303 cam and 24# injectors. Any help would be fantastic before I go buy a A9L
To clarify what Noobz said, if you're running a 70mm MAF, neither of the sizes you gave for TB & MAF are stock to an A9L car. It's also more likely that you have a 70mm throttle body & it's a 76mm MAF, then that would likely be C&L 76mm. C&L used different sampling tubes to compensate for the type of injectors used. So, if you have one, you'll want the sampling tube associated with your 24# injectors.
Double check which specific MAF you have, and determine what injectors its calibrated for (either by sampling tube or if a Pro-M it should be stamped on the black casing). If you have a correctly calibrated MAF to the injectors, and it's meant for a 5.0 fox mustang to begin with, then tuning shouldn't be a must in order to get the car up and running. It's still eventually a good idea when you're ready to iron out idle & driveability issues in the long run, though.