1. Regulate trigger pull to just over 4.5 lbs., the Service Rifle minimum
2. Adjust so that the left and right hammer hooks engage evenly and sufficiently (proper overlap/edge engagement) with both the sear lugs and trigger lugs
3. Ensure that the handoff from the sear lugs to the trigger lugs is properly timed
4. Create a crisp letoff, the "glass rod breaking" feeling
5. Test and ensure that the safety functions properly
All this is in addition to ensuring that the trigger and hammer pins are not worn, and that all the trigger housing parts are properly dimensioned and undamaged.
For full details on rhe procedure, see The M1 Garand Complete Assembly Guide (available from Fulton Armory August 2004). Here is a sample evaulation by Clint of a Trigger Group submitted to him for the NM Modification:
"I got your IHC trigger group today. Your hammer is bad (hammer hooks). I tried to stone them to square them up, but they are just too FU%# up. I really did try to save'em but they are just too short to fix (i.e., I fixed the poor contact surface, but, as I thought would be a problem, the hooks are just too short). It did not feel bad, but only touched on one lug (big gap on the other), & even that one lug was barely engaged.
So, I've put another IHC hammer (and trigger & hammer pins) & finished the trigger job. Now, I'll get it reparked, then polish everything again. I think you'll really like this one! At least I hope you do!"
--and I did!