I am sure that lakes will chim in here.
I know the ford A460 can be over bored to atleast 4.600. It can also be stroked way out. a 4.600 bore and 4.5 inch stroke would make it just under 600 CI
I know there is a company that make safter market iron and AL block that can be stroked out to like 6"s just for the life of me I can't remember then name.