Yes, you can. I just did it on a number of mine. Or at least you can on commercial rifles and Mk II, Mk. II* or Long Lee, which have the bolt-mounted cocking piece safety, as well as on an early commercial Army & Navy Lee Speed with a tang-mounted sliding safety. The only thing is you'll have to change the trigger, sear & cocking piece to whatever it's going into or the receiver-mounted safety on the #1 Mk. III or #1 Mk. III* will not work as there is no safety notch on the Metford / Long Lee cocking piece.