Help on 408 build

I’m just giving the guy my real world local experience with what I believe is his limit on our 91 pump gas with J heads.
Sure I could tell him that my other car with aluminum heads and 11:1 sitting in the next bay of my garage runs great on the same gas... which it does, but I don’t think that would do him a lot of good.
I think changing out the pistons his cheapest solution...or if you only drive the car a few thousand km per summer leave it alone and run race gas.