A replacement or new frame was never available as a spare part in the UKicon. Not even at Enfield/factory/Base workshop level. It was what we call the 'master component'. I realise that the numbers were engraved quite deeply and that would preclude filing or milling out - but mig or tig welding over would be simplicity itself and distortion free. Making good afterwards, bead blasting, phosphate and paint is your answer I feel. But take it from me, an Army pistol without the master number would be.......... Well, it wouldn't get past the door!

Have you used a micrometer along it against a known service one?