Both will probably outlive the car...
& if building new can cost much the same.
However if we are going to play the game & all things being equal:
For period correctness - Iron block
For max horsepower - I'd go iron block
For Racing - Alu block
For road cruising - Either
For my build - Alu block cos' its lighter & it makes sense to me to match the Alu heads and Alu body with the Alu block
