Horsepower with mileage options

For in-town and local roads (which even that varies alot) you could experiment with non-CAP vs. CAP timing and fueling a big difference between the two is at idle. CAP runs leaner but with retarded timing and higher idle speed. Non-CAP probably has a slight edge in fuel consumption. Should have an edge in throttle response too. I'd need to see exactly what pollution controls were used in '71 to have a stronger opinion on that. The Orifice spark delay I think is not until later - that's a real a downer.

You guys remember when GM thought they had a system worked out to drop cylinders at idle?

I think the best you can do in this situation is keep the fuel milage about where it is, while getting a bit more torque and Hp.