Holley carbs and fuel economy are not normally mentioned in the same sentence!
What would be better??? Not necessarily a two barrel.
Before doing anything, do the math. If your proposed new carburetor does 25 percent better than the Holley (and that generally is probable!); how long will it take the increased mileage to pay for the carburetor, and associated extras. Lets say your Holley gets 8 MPG, and you increase that to 10 MPG (25 percent). If you drive 100 miles per week, you go from using 12 and 1/2 gallons to 10 gallons; or a savings of 2 1/2 gallons per week. At $3.50 per gallon, you save $8.75 per week. A quality rebuilt 4-barrel is probably going to cost at least $250. Then you will have a new fuel line, possibly an air cleaner, possibly an intake manifold, etc.
If you decide to make the switch, what you install (or how much it costs) may depend on your current intake manifold. DO NOT attempt to put a quadrajet on a square-bore manifold using an adapter; as this is the best method of causing a Q-Jet to perform as poorly as the Holley! Match the carburetor to the intake (and the engine) with NO adapter. Brand is pretty much up to you, but an original 283 Rochester 4GC (if you have an original intake) is going to outperform ANY new carburetor on a stock 283, both in economy and power; and still doesn't carry the costs of the more popular Carter WCFB. Probably the very best carburetor ever built for the stock 283 was the Carter AFB 9400 (but these are no longer available new, and the demand has driven the price of rebuilts through the roof).
Oh, since you did ask about the two-barrel, expect maybe a 10~15 percent mileage increase over the Holley, provided that you have a stock 283, and replace the intake with a stock 283 2-barrel intake, and use a stock 283 Rochester carb. Trying to install the two-barrel on the four-barrel manifold with the adapter would result in worse fuel economy than the Holley.
Jon.
