Stumbling Slant --what is left??

[1] What heat range are the plugs? Too cold will quickly foul. With such low cranking #s [ did you have the throttle WOT, as reqd for the test? ], I would fit one grade hotter plugs; & they should be projected nose. Champion used to make a plug, the U series, specifically for high mileage engine but I believe they are discontinued. Try NGK 4 heat range.
[2] Fuel pump? Pressure too high causes rich mixture. Unlikely to cause the problem but since you tried so many things, worth checking.
[3] Points ign is not helping. Low on spark energy. Elec ign is cheap & worth it if you are keeping the car. May not cure the problem, but would likely improve it.
[4] Valve guides/seals worn. Replace seals at least, easy to do in situ.