340 Direct Connection cylinder heads

You seem to be referring to w-2's; it would take some work to get them down on a 273, it can be done; big question of cost /benefit. There was/is a version out there that had a 55cc chamber, after notching the bores for valve clearance, you might end up in the 9 to 9.5 range starting with a 10.5 piston.

Big question is WHY???