Aluminum cylinder heads

If it were me I would go with the closed chamber and thicker head gasket, just in case you end up rebuilding your motor or put those heads on another short block you can zero deck your pistons. Let us know how it runs after the change, I have the same type of pistons in my 340 as you do and was looking at the trick flow heads, a little more $ but are cnc ported and ready to run out of the box with good components.