Brake issues - NEED HELP ASAP

Agreed with Shakerhood.
You might need to match up your old switch to the new one if there are that many choices.

There are not many other options than replacing the booster.

Power brake booster test:
1.) Check engine vacuum you should have 14"-18" of vacuum at 625-750 RPM, 18"-21" vacuum at 1000 RPM.
2.) Vacuum checks good, start car and run engine up to 1000 RPM for 30 seconds.
3.) Cut off the engine and then press the brake pedal 3 times. It should get harder to press and travel less each time you press it. If it doesn't, then the brake booster is suspect.

FWIW, I only see one switch on AZ's site. You might have been looking at the generic switches (there were several).

The Mustang switch listed when I look (YMMV) is Duralast F4837

Do you have a Haynes manual? It might have the info for the switch R/R (I know the 94+ manual does for SN95's, but can't remember if the fox manual has the corresponding fox info).