Small Block Stroker ... Gas mileage?
Don't know about 20-mpg.. But with the extra cubes from a stroker, you could run compression that won't need 92-94 octane (regular unleaded) and still make good power.
This is what I see... You want a stroker... You want to run compression that will require the best pump gas... You want to run a big cam... All this = building for power.
See where Im going with this?
These cars were lucky to get 20-mpg with a stock V8.
If you want MPG, build a 318 for it and switch out engines during race season.
Not to be a jerk or anythings but your questions have unreal expectations... Im sure you could get it to do what you are asking but it would require a computerized engine management system and overdrive transmission. All of which would cost more than you would ever spend on the extra gas.