Max MPG- slant vs 318/340

Here's my combo on my daily driver which gets around 20city/25hwy mpg:

Body: 72 dart 4 door w/ 74 duster front clip, no frills, power nothing just a place to sit and steer, no carpet, no radio, extra steel reinforcement behind the front bumper removed, weight unknown but I would guess just under 3000 lbs.

Engine: Stock 72 225 with 170000 miles, offenhauser 4bbl intake w/2bb carter bbd, stock exhaust manifold, 2 1/2" single exhaust w/flowmaster 40 and a thrush glasspack at the end (was too loud and annoying with just the flowmaster) Burns about a quart of oil every 1000 miles.

Transmission: OD 833 from an 82 Dodge pickup

Rear: 8 1/4" w/3.23 suregrip

Performance: best 1/8 mile time I've got so far is a 12.55 @58mph, I would imagine 1/4 mile time would be measured with a sundial.

There's no reason why a good running 318 couldn't get 20's mpg in a light car with conservative driving, with a overdrive transmission mileage should be in the mid 20's.