According to Craig Riesch's U.S. M1 Carbines Wartime Production 3d ed., :
1) Barrel markings indicate manufacture by the Inland Mfg. Div. of General Motors corp. in July 1942.
2) "Some Inland, Underwood, early Winchester, and early Saginaw S'G' carbine stocks will show the 'circled P' proof stamped into the bottom of the pistol grip." (Riesch, p.71)
"RRA" is an inspector's cartouche, I think. There should be an ID code letter(s) stamped in the left side of the sling well in the butt.
3) "J.A.O." is a code for Inland Mfg. Div. used only on the Type 3 rear sight. (Riesch, p. 17)
4) I cannot find anything referencing a number on the bolts...it may be spurious. On p. 18 of Riesch's book, it states that there should be a manufacturer's code mark on the lugs or under the left lug if Underwood Mfg. Co.
Hope this helps!
BTW, the receiver should have the manufacturer's name stamped on the rear, under the rear sight. If you don't mind, look at it and post it here, please.