coming from a dsm community, a safcII is used when going with bigger injectors. its a piggyback system, basically lying to the ecu to get it to do what you want. so if you have larger injectors, youll lie to the ecu telling less air is coming in, so you can run the larger injectors and not flood the cylinders with insane amounts of fuel. this system is not very accurate from a tuning standpoint, i used the safcII and a palm logger for a month or two before ditching it due to its "laggy throttle" feel it got because the safcII cannot compensate for the larger injector dead times. i went with DSMlink and never looked back.
it *would* work just the same on any car. the safc takes the maf/karmen/map inputs and alters them then sends those altered numbers to the ecu.
though im still curious as to why you would need one with a stang.