How is the bushing held in the bolt face ?

It should be welded in by a competent welder and then re-machined.

Bushings can be threaded in, soldered in, or simply pressed in. All methods work.
If I intend to press or solder in I first cut the recess for the bushing with a 5/16 end mill. A depth of about 1/8 is fine. This leaves a substantial shoulder against which the bushing sits. The bushing is made from 4140 and cut to .001 over if pressed in or .001 under if soldered. Pressed in is additionally retained with Loc-tite. Soldered is self explanatory. Since there is no pressure to push the bushing out it isn't likely to come out. I shoot one M70 with pressed in bushing which I did about 4 years ago and which has subsequently worn out a couple of barrels and is still fine.
Another method involves drilling right through the bolt face and tapping it 1/4x28 then a recess is cut and a threaded bushing with shoulder threaded into the bolt. In either case I make the firing pin 1/16 and drill the bushing accordingly. Regards, Bill.

Thanks thats all I needed to know. Art

Bill Leeer is dead on (press fit or solder(hi-force 44)! I would not take a TIG welder anymore to anything on a bolt other than the bolt handle. If you do, it's probably a ruined bolt(usually) and minimally a re-case hardening job. In the past, I have welded up oversize firing pin holes and re-driledl them, but It still involves a re-case hardening or re-heat treating .-Rob

I did specify a "GOOD" welder.