John:
Missed your earlier question about determining proof on an "after-market" conversion such as this, sorry.
The method used in Australia by all gunsmiths I have raised the question with, is to measure everything, then grease the outside of the case of a full-power load with case-lube or anhydrous lanolin or similar, and fire the cartridge. Repeat a couple of times. Remeasure.
This method is generally believed to increase the back-thrust on the bolt, standing breech or breech-block by perhaps 15 to 20%, without reducing any radial thrust.
In the absence of formal proof, the firearm would then be considered safe to fire with normal full-power loads.