The US only put one serial number on an M-1. The other numbers on the parts are drawing numbers. From the drawing numbers, you can tell if the parts were made more or less in the same production period as the receiver. There is absolutely no way to tell if the parts were originally assembled to the receiver. The ex-Danish rifles have serial numbers on the bolts and stocks, which may or may not match the receiver depending on how many times the rifle was rebuilt. At least 95% of M-1 rifles in US service were rebuilt at least once; there are very few M-1s that are all original assembly. The single largest group of these are the ones supplied to Britain under Lend Lease.
As far as D-Day use goes, is there any provenance? If you have actual proof of this, the value would be significant. But it would have to be actual proof, not just a serial number which dates earlier than mid-'44.
The gas cylinder and front sight can be easily replaced, to restore the bayonet lug and front sight ears.