Cutting an inch off of a Garand barrel would remove half of the threads for the gas lock. It would also destroy any chance of getting any real port pressure to the gas cylinder, making the gun a straight pull bolt action - no matter what the bore condition was. So forgive me for not taking this claim at face value.
Plenty of barrels available out there (I use Wilson) as well as barrel vices, receiver wrenches, alignment jigs, chamber reamers etc., etc. All it takes is money..... and lot's of it. Oh, and you can simply swap out the stamped trigger guard on your Garand with a milled one. No need to change the entire trigger group.
Save the old barrel and put it to good use. Cut off the chamber end and make yourself a bolt lapping tool.
I have 4 Garands and have never once considered converting one to a ".308 magazine fed rifle". That's why god invented the Springfield M1A rifle.
Seriously though, I have all the tools and gauges to do it but in the long run it's much cheaper and easier to just buy the M1A and have a better gas system to boot.