408 Build help

Just my opinion:
Since 11:1 compression is to high for pump gas I think aluminum heads might be a bettor choice. However, it still may be a little too high. If you could get dished pistons say a 16 cc dish that might solve the compression problem for the iron heads. You would have to go through all your components to determine that.Bore, stroke, chamber size, gasket compressed thickness, deck height. I have never heard of milling out the chambers but I suppose it could be done. Polishing the combustion chamber may reduce the likelihood of detonation but that wouldn't be enough by itself for your application with the iron heads.