Hello there, shoot a few pictures and that should help answer your questions. Likely a navy fleet marked stock from the sound of it, but if it’s truly unit marked it could be a cut down 98b stock or something. Usually a stock m/m is worth less than a bolt m/m seeing as the original stock is a huge component of the rifle’s value. If you’re in it cheap and just want it to “look” correct then it might not be too bad a proposition to look for a cupped stock, but you probably won’t gain much if anything by swapping it.