i believe that the 336 RC production carried over into the microgroove era though which was about 1955 so it may not have ballard which alot of people would prefer..
"RC" (regular carbine) 20" barrel full mag tube with barrel bands.
"SC" (sporting carbine) 20" barrel 2/3's mag tube no barrel bands.
"CS" (cross bolt saftey) 20" barrel full mag tube with barrel bands and CBS.
Nothing to do with micro groove or Ballard rifling. You have to use serial # or look down the barrel for that.
MG was put in the center fire rifles in 1955-56