Kyle,
I think you said early on that you had an early 90's 5 liter engine. I just got a heads up from the DIYAutoTune folks in my email today about a plug and play version of their ECu for 96-98 mustangs. Yours obviously is an earlier implementation. That said if you get an engine and dash wiring harness out of a salvage yard car this ECU will work for you, click here =>
96-98 Mustang P-n-P ECU
If the early 90's wiring harnesses are too hard to find get a early 2000's Mustang GT wiring harness and use the same ECU but packaged for the newer car and at the same price point, click here =>
1999 - 2004 Mustang GT The software and electronics are identical only the pinouts on the OEM connector are reassigned for the particular year harness you are using.
This approach and one of the Fore hats for the fuel pump and fuel level sender / sensor capabilities will transform your ride into a very manageable very tuneable attitude adjustment car. The documentation on the EFI computer is stunningly complete and the Videos from Youtube give visual confirmation to the written word in the manual.
Replace your existing beat up fuel tank with a suitable OEM alternative, plug in the Fore fuel hat and install the MS3Pro plug and play ECU from DIYAutoTune and put your aggravations behind you.
p.s. One of the nice attributes of the MS3Pro PnP systems is their support for the OEM Ford dash instrumentation. It is always nice when the dash is not dark.