Gas Mileage query Holley 318

An O2 sensor and a air/fuel gauge is the bees knees. I could get over 20 with my 68 dart on road trips after I bought one and started fiddling with the bbd. I had 3.23 and an a 42rh behind a stock 318 from a big RV.
I wouldn’t think a dp Holley would have any disadvantage to any other Holley pertaining to fuel efficiency unless you are into the secondary’s much, but any carter type carb tuned close would probably make an improvement. In my experience the carter type is easier to fine tune.