Funny you should mention the 55 Commander with the 224, I drove one in high school, it was darn near indestructible.

I'll bet the sound of that horn was, well, shall we say, distinctive.

Sounds like timing, hopefuly ignition and not valve timing.

Have you tried replacing the condenser?

Owen's right of course,I wasn't suggesting trying to run on the gas if it is bad, just that is unlikely to be icing.

If you can use a glass container and pump some fuel into it, if there is a separation layer it will likely be mostly ethanol with a little water, it will burn but will not run
well, it will seem to run lean because it takes approx. 30% more volume of ethanol to run properly at a given amount of
air volume. It takes a very small amount of water to make the ethanol separate from the gasoline. But it shouldn't ice up as ethanol is a pretty good anti-freeze.If the problem is like that I had this week, it is because the engine just doesn't like to run on just ethanol.

Be sure and polarize the regulator - generator, otherwise it might even run a little better. Did the ammeter read charge when it was above idle? If it did someone might have swapped sides with the wires.

I would like to mention a recent experience with "modern" gas, l
live in the "boonies" and keep a large generator gassed up and
ready since when we lose power we are among the last to get it back.
I usually keep the tank full, but had not filled it since the last use, about six months ago.
This week we needed it again, when I started it I got a large puff of
white smoke and it wouldn't run without the choke.
When I finally got around to checking the fuel there was a large layer
of what appeared to be water at the bottom, the ethanol had combined
with condensation as the tank"breathed".
Since you mentioned you had one half tank and had been having high
humidity I thought I would mention this since you might not usually have this problem.

Looks like a Super Eight.

Looks like they put 2 primaries on one side and 2 secondaries on the other