5.2 magnum A833 2.93 Highway MPG

What highway mileage are you guys getting with a stock 5.2 magnum with 4speed (64 B&T)?
Planing on swapping out the slant six for a Stock magnum 5.2 RV Camshaft Rpm air gap 500cfm edelbrock, and magnum exhaust manifolds With a solid distributor curve and a good V-Can, and a msd box with 2.93 gears. Hoping to get 20 Mpg on the highway and at least 15 on the street lol.

car is a 64 Dart No power anything with a 245 60 15 tire in the rear.

Why I’m thinking this is possibly is because the magnum has true 9:1 CR lighter rotating assembly roller camshaft better heads and the stock camshaft is a low torque monster lol