62 cc and Open?.....open as in ported or open as in open chambers?......the indy x head is a close chamber head.....
High compression 340 pistons are design to have a positive deck height...meaning the stick out of the bore....close chamber heads not designed to work with that type of piston...an open chamber head is....you will need to increase the thickness of the head gasket which defeats your intend of raising compression..
decking the block will only make the piston stick out further on the block...
you are going to need a dome piston that is design for a close chamber head.....