Open chamber makes more power due to the breathing ability and flame travel. Closed chambers were about 109 cc. Not interchangeable without changing pistons (unless you are flat topped.)
I just went through this with this 540 I am building. I decided to go 119 cc head and do the compression with the piston. Had this been a Pro Stock deal I would have gone the small chamber (113 cc open) deal for max compression. But if the customer wants a blower (and most do down the road....or should I say river ) then the 119 chamber would make it easier to get a piston for blown gas or even blown alcohol. Compression wise. If any of that helps you.