1994 mustang gt misfire

That injector looks like it wasn't flowing much, probably for quite some time. So it definitely needed replaced, even if it wasn't the immediate cause of the problem. If the left bank is being enriched, the O2's think it's not getting enough fuel (too much air). That could be caused by another dead cylinder (O2 sensors don't detect raw fuel, only the air which hasn't been used up in the combustion reaction), and it could still indicate you might have a leaking injector that wasn't #3. Did you check how they all flowed / held pressure when you had the rail disconnected?

Run the cylinder balance test, see which problem cylinder it points you to. If they're all good, then an O2 sensor might be in order since it's just one bank mis-reading.

I hear ya, the EEC-IV isn't the easiest thing to diagnose. The cylinder balance test is very helpful. Have you run that? It's basically part 2 of the KOER test, can be run with a paper-clip if needed (if you don't have an OBD-I scantool). Will definitively tell you if it's missing on more than one cylinder, for any reason, and which one(s).

Bearings are a gold-ish color underneath the silver coating. Could be cam, rod, or main bearings. Not sure if your cloudy oil was a lot of shavings, or coolant in the oil. A blown head gasket might explain your driveability issue, as well as the wet plug (that injector probably wasn't pumping any gas). If it was getting coolant in the oil, it'd chew up the bearings pretty quickly. Or it could be some other mechanical failure or low oil pressure.

Sorry man, brighter side used 5.0's can be found relatively cheap (in the $500 range in my part of the world).