Step one is to swap your electronic ignition for a stock setup, that is by far the easiest and quickest way to see if it is fuel, ignition, exhaust or mechanical. My guess is failing ignition.

I've knocked the lobes off of plenty of cams and it doesn't give those symptoms. Compression test will rarely find a bad lobe because you don't need much of a cam to fill the cylinders at cranking speed. If you could crank the motor at 4000rpm and do a compression test, that would tell you alot!
Intake lobe loss just gives a reduction in power without any other symptoms, Exhaust lobe loss gives less of a power loss, but your car will sound like a Subaru.

If it's not the ignition, I would check the exhaust system, mufflers can collapse, a simple rev to 4000 and feel what's coming out your tail pipe.
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69 142S Overdrive + 69 164S Manual