Aluminium v cast iron cylinder head

[Alan]

I know that theoretically the greater thermal conductivity of aluminium should reduce the thermal efficiency of an engine using an alloy head but in practice I don’t think it would matter much to a 7 engine.
Over the years I’ve played with many cylinder heads and to be honest never really seen a marked improvement over the ‘37 head. Provided your bores and rings are in good condition I’d use one of those with 60 thou or so shaved off.