The vast majority of 1903's "sat out" WWII and Korea, so your rifle sitting out the war would be a normal event. As for the scope blocks, I have several 1903's with those bases mounted, and not one of them is a USMC sniper rifle. As for experts, you have the foremost experts in the USA on this forum, and all of them are willing to help you. Post pictures so they can see what you want them to judge as fake or real. You will get a fair and honest appraisal of your rifle.
I am a data collector, and I record the serial numbers and descriptions of military scoped 1903's, including a large number of the USMC Unertl scoped 1903's, and your serial number is nowhere near them. I do not claim to have them all recorded, but for yours to be one of that elite group, it would be an oddity indeed. I wish you luck in your search, as I always wanted one myself; but alas, I am but a poor man. If I can help, let me know.
jt