Which carburetor have you got? The Holley 1920, perhaps? I've posted before about a Holley 1920 I once had on my '65 that exhibited strange behavior: The engine ran very well and had fine power, but was suspiciously easy to start and drive from cold (zero choke required, just hop in, turn the key and drive off without any stalling or gasping...even with the choke disconnected!) and the car was getting under 10 mpg. Turned out the brass seat ring that retains the power valve check ball, had fallen out of the metering block. Result was that the power valve was always WIDE open. I put the metering valve back together and restaked the seat ring, and things went back to normal (20mpg, choke and careful cold driving required).

Well, I do have a Holley 1920 (almost 100% sure, because I had to get a rebuilt one a couple of years ago

I just looked at it, and the valve is not wide open... it appears to me to be closed, or as closed as it can get (while still being open a little bit). I moved the rod that leads to the thermostat and all appears to be working properly, so I'm not even sure what "ring" it is you're talking about, but all appears to be there, at least to my inexperienced eyes.

It's also been rough idling a lot lately, like almost shaking the entire car. I noticed this again on my way home from work tonight. Back to the oil... When I check the level on the dipstick, it's actually above the Full line, even three hours after it was last driven. It's all the way up to the "F" on the dipstick, actually (about a quarter inch above the line). And I haven't added oil in months. It's last oil change was in August or September (I know, I know...), yet the oil level is above the full line? And yeah, I think I do smell some gas in the oil, so I think Doc may be correct in his assumption that the fuel pump is leaking into the crank case.