I don`t like Edelbrock carbs, not a big fan of Holley`s either. Most holley`s come with straight leg boosters, these aren`t as bad as down leg boosters however, as dog legs are completely worthless.
A annular booster carb is perferred. It gives it better throttle response and real nice manners. However, annular booster carbs are more expensive.
I perfer a Quadrajet carb and they are pretty much all I use.
Not to say a holley won`t work for you as it will. So if you want to go holley by all means do so. The only cheap carb with annular boosters I know of is the summit racing carb, however you have to get the carb that`s a mechanical secondary which would work fine for what your doing.
How to improve mileage, first off, with a 3000 stall and the low gear good mileage isn`t to be expected, however you should be getting better than 5 miles to the gallon. What`s the timing set at? What plug wires are in use?
First off, if you haven`t already, get the process started by packing the front wheel bearings with synthetic grease. Then fill the rear with royal purple or other synthetic lube if you haven`t already. If your not running synthetic oil swap over to it. Lowering resistance is the first step in the right direction. To get decent mileage you have to keep the revs down which is difficult with your rear gears. You could somewhat defang the engine by going with a smaller cam such as the comp 268H which will still give it a lopey idle, but it`s duration figures are on the mild side. With the heads and combo you have it would still have good power. Then you could switch to a lower stall converter.