So the 65cc heads are an open chamber design to clear the piston. The only pics i could find of them looked like closed chambers but maybe that was a generic pic?
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One phone call will give you better answers than any of us can give you. He kindly answered every question I had for him and if I was still in the head porting business I would have grabbed a few sets.

If you scroll through the pics at the top of the page it shows two chamber designs. I'm not smart enough to know if the one is big enough to clear a 340 piston with the right head gasket thickness. However, it seems silly to go through all the work of having two designs with 2cc difference if not. Maybe I'm all wet so call first as suggested.

https://promaxxperformance.com/product/shocker-185-mopar-cnc/

Seems that the 340 piston was .018 or so above the deck, why not just run a .054 fel pro and have .036 quench distance? If that nu number is not exactly right you can order different thickness gaskets from different places but I am sure that .018 is close.