Compression ratio - I agree with the very high compression ratio approach for this project. Say 15:1 if you can actually achieve it. As has already been stated with small throttle/openings the effective comp Pressure will be comparable to say 9 or 10:1. I reckon this will be the biggest single improvement but you'll have to be disciplined not to use full throttle or risk severe detonation. High octane pump fuel.

Carb - small (1" ~ 1.25") SU type carb as these are very fuel efficient.

Exhaust - extractors, wrapped for heat retention/gas speed, and with std bore outlet (not 2" as this will be too large to maintain gas speed at low rpm/low throttle openings.

Camshaft - std cam (if not an even milder design).

Head - round port head with the most efficient high swirl combustion chamber design (maybe A12 roundport head?).

Hot air - I'm not entirely convinced on the hot air for economy vs cold air for power theory but it would be easy to experiment with this once the rest of the engine is set up.