v6 mass air and injectors with a v8

You need to get the numbers off of the injectors and confirm that they're 30 lbs. Just because the injector is red doesn't mean it's a 30 lb injector.

The trim of that MAF (the way it's "calibrated") is designed for the computer in the Ranger. You can hook it up to the Mustang and it may work but it will be far from optimal and may cause the computer to drive it self nuts trying to compensate. The only non-stock Ford MAF meters that are compatable with the Fox computers are meters with F2VF at the beginning of the part number. You would still need to use your stock 19 lb injectors with those MAFs.

The MAF body and sensor are designed to match each other. Type A sensor works with Type A bodies. The bodies and sensors are not necessarily calibrated together to create a precision matched pair. Therefore you can't swap sensors between different part number MAF bodies and maintain proper calibration.

The output voltage of the MAF is a function of the air flowing through it. The MAF itself does not know about injector sizes, nor does it care. All it sees is that an increase in airflow means a corresponding increase of MAF output voltage. Altering the design of the MAF body can alter the flow past the sensor.

The OEM ford system was designed to use internal computer tables to match the voltage output of the MAF to a calculated injector turn on time. The injector table uses only one size injector in its calculations. This is a much more accurate means of determining the engine’s fuel requirements. Using a different MAF than the one the computer was designed for can upset the computer's calculations and the air/fuel ratio.

What aftermarket MAF’s do is try to fool the computer by either changing the amount of airflow over the stock electronics (C&L method) or by altering the sensor itself (Mass Air Systems method). The goal for both methods is to change the output voltage of the MAF so the computer calculates new data that is used to vary the pulse width sent to the injectors.

I doubt those injectors are 30's....
Pull the part numbers and GOOGLE them.

As for the MAF... it's already been stated...

Measure the ID of the housing, and post up the part numbers you see on the sensor.
Very unlikely that it will be useable on a Fox ecu though... even if you use those injectors.

The factory ecu has a Calibration for the MAF, and another Calibration for the injectors...