It appears you have an early, low number rifle fitted with a later barrel. I think if it were me, I would take it to a gunsmith to have the headspace checked, in case that barrel was not installed properly. If you have one of the old cases fired in the rifle I would take it along, also.
Ask the gunsmith his opinion on shooting it. I have heard both sides of the story; early ones should be wall-hangers, vs. hundreds of thousands of them were used, with very little problems, and of those that had problems, most were probably due to obstructed bores.
If given the go-ahead from the gunsmith, I would definitely use only mild loads, like managed recoil, or reloaded equivalent.
Mark