Back before the days of super-high ratio overdrive transmissions and high-geared rear ends, that was considered to be a very high-speed rear end. I remember driving a 58 Chevy Delray with a 3.70 gear, and when I switched to a 3.34, I thought I had a high-speed rig! Your 2.73 ought to work well, and give you good cruising speed, and also good acceleration. Unless the 283 has a radical camshaft and/or a big 4-barrel, I'd expect gas mileage in the high teens or low 20's. Go for it!
Jerry
