One thing you might want to consider, one time I was in Thomas Bland's shop speaking with the gunsmith and in discussion of my Westley Richards "Improved Martini" of near similar vintage and also with an internal hammer/firing pin he pointed out that the block was soft and he had seen one that had been converted to 22 Hornet have the Hornet's head back right through the block. I suppose that with the block cut to have clearance for the hammer/pin the the area around the firing pin hole is thin on metal and with a small cartridge head supplying concentrated pressure it could give. Maybe hardening would help. Anyway a neat action.
