Bud,

I don't have any reference material with me now but the A9L sounds like the standard 5.0 HO computer for a mass air, 5-speed car.

REGARDLESS, you already stated correctly that the 5.0 HO and the 351W have the same firing order... 1-3-7-2-6-5-4-8.
ALL (86 - 95) of the EFI 5.0 HO's used the 351W firing order.

Your question suggests that you have not purchased a wiring harness and computer. If that is the case, you will definately be better off with a mass air set up. That would be from a 89 and up Mustang harness and computer (also the 88 California cars). Having done a 5.0 EFI swap, I suggest you get an entire donor car as there are many sensors and parts you will need form the car. One last suggestion would be to get the Ford EVTM for the year of your donor car. The Electrical, Vacucm Troubleshooting Manual will cover all your wiring and EFI parts questions.

Regarding computer tuners, the 5.0, mass air, EFI system is extremely adaptive. Unless you get very radical (and I guess that is subject to interpretation) the factory computer can be made to run very well with a lot of aftermarket parts, so long as you use compatible and properly calibrated parts. I am running the factory computer (without chip or tuning device) in my 91 (see signature) and it has aftermarket heads, intake and Vortech blower.

Good luck,

TC