I believe G is for 1949.
Looks like a nice one. The butt plate is not original as you have said. Pachmyer and others make trim to fit recoil pads that work well if you want to change it. You can probably get pretty close with a standard pad too.
Below is a link to the Limbsaver recoil pad templates. You can print them out and see if one will fit.
http://www.limbsaver.com/2010/pdfs/t..._templates.pdf