Stepson has a beautiful Winchester built Garand. He read about a stronger operating rod, ordered it, and we installed it. I did a load development, not on .30-06 data, but on Garand data. It's not what I would call a "Lite load" but it is lighter than what I would put in a bolt action. Got it shooting 1" at 100 yards, with battle sights. We quit right there.
As far as the muzzle thread, most gunsmiths could probably do it.
800 Yard Steel Range Precision Rifle Instruction Memberships and Classes Available
Here is a thread that explains a couple of ways to do it. I guess my only question would be why? The cost of a barrel, gunsmith modifications, and extra parts would be as much as a new bolt gun with the barrel already threaded. Pretty expensive cool factor. I would think any machine shop would be able to do the work for you. As far as headspacing the barrel i would think any gunsmith worth their salt would be able to do it.
Texas LTC Instructor NRA Patriot Life Benefactor Member NRA Instructor in Pistol, CCW, PPITH, PPOTH, Shotgun, Rifle, Reloading, and a NRA Chief Range Safety Officer
Ehh, Garands were made in the millions. If you've got a gun without an interested provenance like a CMP rack grade, you have my blessing to thread that puppy. But my stipulation is that you also need to do an M-14 magazine conversion.