I have 2 late (1955) Springfields and a H&R (1956). As Vern said these late M1s had all the improvements made. M1s got better as they made them and the high SNs were the best.
The H&R I recently got from CMP came with a new Boyd's stock that is very tight. CMP did the equivalent of a bedding job for the price of a SG.
The H&R I recently got from CMP came with a new Boyd's stock that is very tight. CMP did the equivalent of a bedding job for the price of a SG.