those Shebbies oh man... If I was richer, I'd go for it. Maybe find a 3 speed auto to pit in it, so the wife could drive it too. (Had an Escort wagon with a 5 speed manual, for a while. The wife never did get the hang of it) Not sure what the mpg's are from a GM 6. The Fords ran about 16 to 18 city, depending on the car they were in, and 24 or so highway. Not bad for a big old wagon...
My '65 Biscayne sedan returned 18-22mpg in mixed driving with the 230cid six and 3-speed, no overdrive, and I was 16-17 at the time so I wasn't gentle on it. According to some online sources, a '65 sedan weighs 3505lbs and a '62 wagon is right at 4000, I'm guessing 16-20mpg is a good range depending on how many stone your foot weighs.
This looks to be a pretty good buy. If it's been a lifelong Colorado car, there should be very little rust in it. That Stovebolt Six is a very good engine, and with the 3-speed manual, it should return 18-24 mpg on the highway.