IMO, there is nothing wrong with a stock cylinder head besides there weight. Ultimately, the valve lifts so high and the amount of air and fuel that the engine can ingest is limited by the intake track starting at the air filter. Maximize the ability of the air filter, carb, intake, cylinder heads and the best will shine through.
Considering how high the cam is lifting the valve, an iron cylinder head can flow very well with the lift the valve is seeing. A move to an aluminum head is most likely a win, but at what cost? Can a bowl ported factory iron perform great? You bet. But the cost factor has to be worked into it. If your doing the porting yourself, they could be a win. The key here aside from cost is the ability to closely match or exceed the prospective aluminum heads ability to flow air and fuel in the amount of valve lift your set up has.
The engine doesn’t know or care what the heads material is made out of. Your wallet might know the difference!