forced Induction cylinder heads

As far as I know, there are no as cast large open chambered aftermarket heads. You could search for a older set of W2 heads and run them as is, stock, if they can be found as cast, stock &
unported, they flow pretty good.
(Draw back, expensive rocker arms.)

I don't know how far you can open up any aluminum head in the chamber.

Working on iron heads is time consuming making them expensive. The 308 is a good OE head. Better when ported.