Need advice rebuilding a sporterized 03a3

[JAustin]

This is my first posting ever so be gentle. I have this 1903A3 that my father bought back in the 60's. It's sporterized. There's no top handguard and the stock has been cut back to make it look like a hunting rifle. Until recently I thought I could buy a new stock and handguard along with the end cap, retaining ring, and so on and I would be up and running. Today I was looking at a schematic and noticed there's a ring between the receiver and the barrel that holds the rear of the handguard. 1.) Am I correct that the barrel must be removed in order to put the ring there? 2.) If so, does the absence of the ring now mean that it's not properly headspaced? 3.) It shoots fine so I would assume that it's headspaced correctly so does this mean that it has been machined to compensate for the lack of the ring? 4.) If it's been machined, then is the barrel going to headspace correctly if I have another ring put it? 5.) Can the barrel be removed without damaging the finish? 6.) The receiver is dark gray parkerized while the barrel is more of a greenish tint. Both appear to be Remington parts. 6.) Does this mean that it's a rebuild? Sorry for the long question, I'm just going through a strange phase where I prefer bolt action military weapons with wood to the high tech black plastic autos.