1. Mass air didn't hit the market in the 2.3L 'stangs until 1991
2. With a custom burned chip or ECM, anything is possible.
3. Cold air intake, 24lb/hr injectors to support your other mods, a 110lph fuel pump would be a nice step up, eliminate all the smog junk you can (make sure your chip or ECM supports the lack of emissions gear) go with the later mass-air DIS-ignition and 8-plug cylinder head before all else (just switching to DIS, Mass-air, and the 8-plug head was worth 17hp from the factory over the previous vane-air/distributor/4-plug setup).
You could also use a serpentine belt setup (if not doing so already, also note that the only difference between the serpentine and v-belt water pumps is shaft diameter (they turn in the same direction, I drilled out the center hole in my serpentine pulley to used the larger shaft diamter pump designed for the old V-belt system for durability.) I'll be posting a tech article in the Mustang II tech forum on how to convert to serpentine from V-belt in a 2.3L Mustang II fairly soon, procedure would only be slightly different in a fox-body (and you'd retain power steering if you wanted, not room for it in the II without more mods than I was going to do since mine already had a manual rack).
You can also run the same MSD TFI blaster coil as the 5.0 cars use on an EFI 2.3, run NGK Vpower or Bosch Platinum plugs (the ONLY two engines I've ever found that ran well with Bosch Platinums are Ford 2.3s and Mazda 2.2s, go figure, everything I've ever owned has run great with NGK V-power plugs though, including my modded 2.3).
You can also run the same cold-air intakes as 5.0 fox-mustangs in general with a 2.3 with a few changes to make them fit right, or Autozone carries a complete selection of elbows, fittings, hoses, and couplers to make your own these days (already used one of their chrome elbows to repair a system I built years ago using a rubber elbow that had dry-rotted, fit great, looks great, and has held up so far.)
There is nothing you can do with a 5.0 EFI that you can't with a 2.3 EFI, it's just harder to find the parts, and sometimes you have to make your own. But hell, that's how hot-rodding got started in the first place! I've built more 2.3 pieces than I've bought, and modified more pieces from other cars than I've found that were originally for one!
