OK, so some things are likely fine from my list. Let's look at # 3 on your reply. Stalling over 80C engine temp. Put an ammeter in the EHA circuit and watch what happens during this event, and compare that to behavior below say, 60C. Are you leaning out purposely ( lower and lower current readings )? After obtaining the readings, put a resistor in the coolant temp sensor line, say 250ohms, and try again. Did the problem go away? If so, the temp sensor or its related wiringis not giving a true picture to the computer.
Second part of the check: Vacuum readings at idle, cold and hot. The engine needs to draw enough air to keep the sensor plate deflected or it shuts off the flow of fuel. IF you have a temperature related vacuum leak, such as a cracked casting, or a valve with too little clearance, heat will affect its performance.
Idle switch, A/C switch, etc. Make certain you're actually activating the supplemental idle control switches. IF the AC cycles on without giving a signal to the computer, you'll lose 5hp, and about 100 - 200 rpm. IS it dead yet?
Your # 4 response: If you can't get to the factory timing marks when running ( it's difficult on a 2 valve, but can be done), you should still be able to see them with the engine stopped. Get to TDC1 and put a mark on the cover and pulley wherre you can get at them with a light. Also mark off a second line on the pulley at 10 BTDC by measuring the distance with a caliper and transferring it to your new marks location. Then you can perform a visual check of timing location. Timing delayed by 5 - 7 deg is enough to give the system problems in meeting idle emissions, so it will keep leaning the system out to try to get to a good lambda reading.
Your #1 Fuel distributor failures come in all variants. A little cross injector leakage, or a marginal bleed volume to the pressure regulator could result in idle loss. Are you really dead perfect on the two set heights (zero and stop )?
Your # 5: This is part of what I was talking about with an idle test. The best way to do this is with an electronic, digital tach and an electronic cylinder shorting system like many diagnostic systems have. You're looking for say, 150 rpm drop at each cyl. If one drops 10 and the rest 160, you've narrowed the search to one suspect.
IF you go to open mode ( bypass the O2 sensor ) what happens?
Have you done the two primary O2 sensor tests?