340 High Compression Pistons

BTW, have you considered using standard flat top pistons and just milling the deck to the get the pistons enough above deck to protrude through the head gasket and into the milled part of the chamber in the same fashion as described above? As an example, KB243's would require just another .020" of block milling (.035" total off of standard deck height) to get them .053" above the deck. And there are probably others that would work. The same could be done for any standard CH 340 piston.

And BTW, I see that the JE piston like you linked above has 6.8 cc eyebrow volume. So the SCR will drop around.2 if that eyebrow volume is used. And putting a chamfer on the edge of any piston top would be wise in this type of setup IMHO, to avoid a sharp edge that will get hotter than the rest of the piston crown.