US Springfield Armory Model 1903 - What can you tell me?

What I think I know.

-) S/N 68524x for a 1917 mfg. date.
-) The stock has a “J.F.C.” final inspector mark (for J.F. Coyle) in block letters inside a rectangle.
-) "S A" Springfield Armory stamp at the top of the barrel along with the flaming bomb and “7-42”
-) “G” on the right side of the sight.
-) “C64157-4” on the left side of the sight.
-) “H” on the bottom of the upper band barrel support means “Hardened”.

Mostly Correct?
What is "G"?
What is "7-42"?
What is “C64157-4”?
Is it common, not to have the "P" mark?