Good afternoon
I understand your frustration troubleshooting the SC. Don't give up. I had a SC with the same problem that had not run in 8 years. It was a fuel system problem. Is the exhaust manifold still "cheery red" when running? If so address and or eliminate the fuel issue. Did you accomplished the fuel pressure rest (or residual) pressure to check leaking in the system? To check leak down pressure (residual):
(1) Begin with the engine idling, with the fuel-pressure gauge connected. Get ready to time the leak down.
(2) Turn off engine, the turn key on, but do not start. Observe the Key On Engine Off (KOEO) pressure.
(3) Turn the key off and measure pressure for one minute (should not lose no more than 2 psi per hour) after turning key off.
(4) At the end of that time, fuel pressure should hold within the KOEO specification. Did it pass?
Did you remove the spark plugs of visual inspection? Check for too hot condition. Blistered, white insulator, eroded electrode and absence of deposits. The Ford Thunderbird Mercury Cougar Haynes repair manual 1989 thru 1997 back cover has picture of this condition. Or you can refer to the internet.
I agree with Mr. 820 in regards to contamination the fuel injectors. The fuel rail and injectors must be cleaned. Start first by visually checking the condition of the fuel (take a sample). Is it cloudy? Floating crud? If so all of the fuel will have to purged. If no problems here are some options.
(a) Remove the fuel rail. Have shop professionally clean individual injectors off the car (best). Flush the rail yourself.
(b) Have a shop use a pressurized fuel injection cleaner for the injectors with the car running.
(c) You could use a very good off the shelf fuel system cleaner. It will require more than one application and a fuel filter(s) change.
(d) Clean the fuel rail and injectors yourself. Refer to you tube information on how to accomplish this DIY task.
(e) Clean the MAF.
(f) Do engine scan.
Good luck.