Since your car runs fine with disconnected MAF it means that fuelling and spark side of things are fine as it runs ok using default map, without looking at sensor inputs, even if its rich. I would concentrate on various sensors, one of them is fouling and reason for your misfire, sadly no OBD here so you'll have to resort to either measuring signals or substituting things. It will most likely be fuelling related issue so you should start looking at o2 sensor, coolant temp sensor, TPS and MAF itself. Just to confirm what MAF are you running? Check voltage on the CTS when engine is up to temperature, we should be able to translate it for you to something relevant in C.
You will also need to check TPS voltage and confirm that it runs ok in full range from 0.6V when closed to almost 5V at wide open throttle, key in position one is enough to check its voltage, you don't need to run engine to get the readings.
Check MAF plug for continuity and any broken wires, make sure it isn't messed up.
o2 sensor if its old, probably best to replace anyway, if not, you might be able to check it with either an analogue multimeter or you might have to resort to using an oscilloscope.
Failing that, next step would be to find a substitute ECU and possibly checking injectors for either leaking or poor patern(both common issues)
You could also check fuel pressure, or at least pinch return line, when its running, see if it improves things in any way.
1996, 3.2 SWB X300 - Relatively rust free daily driver!
1997, 4.0 LWB X300 - Unlucky car, sold 10.2020!.
1988, 3.6S XJS - Never ending restoration project.
1994, 3.2S X300 - Accident damaged, 10.2015. Gone!
1994, 3.2S XJ40 - First Jaaaag, long gone.