Nothing wrong with the Q-Jet. When tuned properly, they're actually a very good carb. Most people who say to "chuck the Q-Jet" don't know how to work on them. While the Holley is an exellent carb, as is the Carter AFB (I've heard the Edelbrock version sucks, though), the A-Jet is the way to go for feul mileage. You'll see better mileage with that carb than even a 2 bbl. Most who say to use a 2 bbl for mileage simply don't understand how the Q-Jet works. During normal driving, you only run on the primary throttle bores, which are actually smaller than the bores on a 2bbl. This uses less feul. When you need the extra power, though, the rather large secondaries open up (about 75% throttle), and you have all the power you need.
If you want to overhaul the Rochester, do these 2 things first. 1, get a high quality overhaul kit, preferrably a Genuine Rochester kit, if you can't find one of those, Standard-Blue Strak makes a good kit as well. 2, get a shop manual that covers your carb. You may also want to check out HP Books, they have several carb manuals, including one for Rochester tuning.