Although this is an old thread, I may be able to answer your question. Your M1 was manufactured sometime in 1940. LMR barrels were used in the early to mid 1950's, and almost entirely on IHC's. Your rifle has been rebarreled at least once in the past, possibly more than once being such an early reciever.
You should have a good shooter since LMR barrels are well known for exhibiting more than average accuracy.
Congrats on your very early M1!