rdorman,
I think looking at your plugs is going to give you the best indication of whether or not you're too rich or lean. All that black smoke sounds like gas to me. You did say that you were using
oil, but you could be losing it through valve seals, like you said.
My Cleveland was built in AZ and, due to the fact that it sat for a while in the dry air, I had to replace every valve seal. I was going through a quart of
oil every hundred miles or so until I replaced the seals.
Cheers
Jim