I rebuilt 100596x and have saw an original 100963x. The original one came out of a barn from a stack of rifles. When my friend said he wanted to buy it the lady said you have to take the whole stack. How much $200. Gee can you do better. Nope. Oh well, OK. The owner has been offered $5000, but won't sell. See if the CMPhas a barreled receiver with a serial number close. Rebuilding it is not bad. Only the rear sight is the hard part.
Good luck. I have been looking for my father in laws rifle. SA 1523350. Carried it when the 63rd Infantry Division pierced the Sigfried Line. I found one at a show 20 numbers off. It was a Korean War rebuild. I've been looking for 10 years now.