Milling 360 heads for a 318

What cc would I be looking at if they were milled like say .040? And it's going to be just a fun driver. Not looking to really race it. The plan originally was to get a 408 but that's probably going to be next winter. I really just wanna drive it so I'm throwing the 318 back in but want more power. I already have a performer 318/360 Intake, headers and I think a bigger cam was put in at some point. I may put a cam in to not sure yet. It's got a 4 speed and unknown gears. I plan on swapping like 3.50 in so I can take it on the highway occasionally.