Nice rifle and they are a boat load of fun to shoot. I'm not an expert, but have two miyself. Stocks replaced in the field, or any stop shoot of the arsenal, were not proofed and tend to have no markings. I suppose it could be an aftermarket stock. If it had been sanded enough to remove the markings, it likely would show in the areas where the metal meets the wood. Like the buttstock would overhang the wood if it had been sanded significantly. Early Remingtons had pinned stocks. I see yours has stock bolts. I would accept it as is. A nice looking rifle with a replacement stock. How does it shoot?
Now the fun starts. Start looking for the 'R' marked parts. Things like sling swivels, barrel bands, and all of the bolt parts. Remington formed the barrel band spring relief differently than Smith-Corona. I can't remember who used a square cut and who used a rounded cut.
I'm hoping someone who knows more than I will come along.
Nice rifle. Have fun shooting it.