Poor hot idle caused by ethanol gas? Whaddya think?

You are 460 miles south of me, and only a little lower in elevation.
In 1994, I got me a 1980 Volare and only sold it about a year ago The slanty in it, since 87E10 came to town, always started/ran perfectly on it, year round ; 87E10 is not your problem.
My slanty had a Carbon canister but the vent-line rusted out. and yes it had an EGR. I installed an older solid lifter cam engine into it before I ever drove it, on account of I got the near-mint car with a blown engine for $100. It turns out that the rearend was also blown, but I did not know it, lol.
IMO:
87E10 is Not the ogre everybody likes to say it is. I have been running it in my carb'd 367 68 Barracuda since 1999. Granted the entire fuel system was brand new that year. Late this year, October, I fired it up and took her for a spin, on fresh 87E10.
IMO:
your problem is a rich condition. Take a couple of plugs out and look.
So then, if I am right, you just gotta figure out why. That could be simple or it could be ridiculously hard to figure out.