360 running on 4 cylinders

I spent the day troubleshooting and am no further ahead. Could it be valve timing?

I pulled plugs and measured compression, it varies from 115-125 across all cylinders. Not great, but not bad. It's a stock bottom end so it will have low compression.

The plugs are all black now with the Holley installed, running really rich. Tore it apart, cleaned it up with carb cleaner, set the floats and idle mixture to factory recommended settings, ran a little better but still rich as hell (I now have a headache). I'm not convinced it's a good carb. Anyway, installed a fuel pressure meter and it's running about 6psi as expected at idle.

Measured spark gap, it's about a 1/4 inch maybe more.

Put on a timing light just to see if it moved for some reason, nope. Initial 12 degrees all in 32 degrees.

Sprayed water all around the intake manifold, no change to idle.

So here's the symptoms again. Car was running fine since the spring, took it out for a few short highway trips around 100 miles round trip. No issues. Decided to take a longer trip and about halfway there noticed the sound of the engine changed, it had a bit of a shake at highway speed. Pulled into nearest town and it wouldn't idle. Limped it home, it still maintained highway speed ok but no power. Thought it was the old Carter since half the engine was cold when idling (180 degree dual plane intake). Replaced the Carter with a Holley 750, same problem but now with added bonus of running too rich.