cast iron heads vs aluminum for stroked 340

It's not that the goal build is unrealistic but it is a odd one. Like mentioned, Mike at MRL has interesting engines that should be looked into.

Otherwise, the only iron head(s) worth looking at are the Indy or the more capable W2.
For aluminum, well done Edelbrocks will turn some numbers. There's also Brodix. B1BA-MC.
W5's are a crap shot. Only worth IF the can be ported out to what you need.