Wrong answer - only after market MAFs are calibrated to the injector size. Since it is easier to lie to the computer to get it to think that more air is flowing by modifiing the MAF signal output, that is what aftermarket MAFs do.
Every Ford MAF made was calibrated to the computer. The computer's program contained the calibration for injector size. The Cobra computer's program is calibrated for 24 LB injectors. The MAF has nothing to do with the injector size.
If you want a 70MM Ford MAF, here are some that are an exact match for the A9L or A9P computers found in most 89-93 Mustangs, try one of the following:
94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2
*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
The last 2 or 3 characters on the part number (A1A, A2A, AA, AB, etc) are not important and can be ignored. They represent minor changes that have nothing to do with the operating specifications.