According to Brophy the illustration in the TM 9-280 is not of the M9122 but is of the prototype M1920. The M1922 was manufactured with the headless cocking piece. I believe that the bolts in total are interchangable but of course the headspace would have to be checked. It is indicated in Bropjhy's book that rifles returned to the armory for repair were brought up to the latewt configuratiion. If your rifle has the double pointed striker, it may well be original.
According to Brophy, the M1922 scope blocks were mounted on the barrel at the armory, not the receiver. From your pictures, it looks as if there are scope block holes in the barrel just forward of the receiver. If so, the receiver mounted block may added after original manufature.
I still believe that your stock may be the original stock, "reworked" by a gunsmith.
The Lyman 48 is a very erly 48
I am not a collector so do not know how much the "modifications" detact from the rifle. Some M1903 sporter conversiions are works of art and command a nice price, even if modified. It is still a nice rifle and a relative (I think) piece of history.
I hope this clarifies my previous posts. I was relyig on government publications to be correct. Evidenlty it is not. I have both the 1 Oct 1940 and the 16 March 1944 editiions of TM 9-280 and both have the same description of the M1922.