I believe that it is the failure of the used prechambers and related parts to effectvely seal in the milled recesses of the new head that is the actual problem causing the lack of compression described due to leaking in the first post.

At issue is correcting that failure to properly seal while at the same time ensuring the proper clearences both below (into the combustion chamber) and above (extension of the prechamber and its' sealing ring above the head recess surface)

Apparently the machine work on the new casting is different (worse?) than that of the original casting leading to compatability issues with the original parts. I'm following this issue as I anticipate a possible head replacement in the future.