Joe, More data would be nice(especially for people who collect data sheets on early pre war rifles) such as your bolt heat lot, type of firing pin, polished bolt face etc.
I really do not know if your rifle is original or not - it looks like it could be original- but remember that back in 1975, Rock Island Armory was in the trade-in program with the NRA.
For around $21 and your old
M1
receiver (welded stuff not allowed) you received a like new or as collectors would say "mint" M1 receiver with barrel. I had a friend in Texas that got a Aug 1941 barrel and receiver and another friend in Minn that got a 405xxx with S-A 12 41 barrel. Also saw an early 1943 barrel/receiver, barrel had a TE of 1.0. None of these barrels had chrome on the gas ports.
Some Lend Lease rifles had their parts "harvested" to build-up "correct" period rifles and a late 1941 SA rifle in excellent condition was worth more than the Lend Lease.
Robert