building a long distance touring car

Looking for straight mileage over performance is easy, generally small displacement tall gearing and tires and slow driving speed. Eg. 170 /6 2.76 + OD and 28" or taller tire at 55 mph.

But with performance it becomes slightly harder.
First I see displacement in more of dynamic thing, its only static when the engine is off. Cid x rpm / 2 = dynamic Cid or as we normally calculate it in cfm = cid x rpm / 3456.

Take a 500 cid engine cruising at 1500 rpm equals 217 cfm or a 250 cid engine cruising at 3000 rpm equals 217 cfm both would make similar mileage and if makeing around the same hp would also be similar in performance.

The advantage of the larger displacement is good performance with lower cruising speed and probably better street manners.

That why Id pick 360/5.9 cause its the largest stock displacement small block you can get. See no point in stroking an engine for this performance mileage level.