A black bottom magazine would be a 'correct' replacement by say, a unit armorer - it is very common to see miss-matched aluminum or even wood bases with WW2 guns.
I always call it a locking bolt spring, but I bet your terminology is actually correct, sure would not be incorrect.
I'd love to see the magazine bottoms, sometimes an 'extra' mag can be worth $125 or it could be worth 2x or 3x - depends on what kind it is
I don't collect this era, although I have a 1939 police from a friend and he brought it back from WW2, I don't have any bring back papers. BTW, you can look up (if lucky) the soldiers name in the records and get basic info on them. By name it might come up with several same names, if it ha his army serial number, it has a good chance that we can look it up
http://aad.archives.gov/aad/
Ed