Nice pistol.
Serial number, A1 features, and the fact it's a Remington-Rand looks like a 1944 production pistol.
Sinister is correct, that pistol was made in 1944 based on the Serial number.
I really wouldn't loose a lot of sleep on the "not all original parts" gun. Contrary what you read on the internet, there are few of those in existence. The 1911/1911A1 were designed to be plug and play, meaning parts interchangeable.
Back in 1966 I went to MP AIT. This other guy and I screwed up one day and while everyone else had the weekend off, we got the pleasure of taking apart and cleaning all the MP Schools 1911s. And they were a lot of them.
We field stripped the guns, laid them out in an assembly line. Frames here, slides there, barrels in this pile, etc etc. Then he started at one end and I started at the other and we cleaned all the parts. Then we picked up a frame and walked down the line picking up parts and putting them together, we had no idea nor cared what parts went to what frame.
Fast forward a couple decades. I was running the AK NG Marksmanship Program. We had a "combat" program where units competed using arms room guns. Issuing arms room guns and marksmanship guns come under different rules. You can't take an arms room gun home but you can a marksmanship gun. So I ordered a bunch of 1911s so I could issue 4 to each BN and Separate Company, Plus kept 10 on hand to issue the winning unit so they could compete in the Wilson Matches (NG Championships). Before issuing any guns I had my best pistol shooters go through all the guns switching parts until they came up with the best and most accurate 10 guns to keep for the State Team.
That is only two incidents on switching parts on 1911/1911a1. I'm sure I'm not the only one who switched parts. My personal 1911a1 was thrown in the pile so its parts could be switched around like the Guard guns. It now has a USSC slide resting on a Colt Frame, but its shoots darn good for a USGI 1911a1. I have a second slide for it that has high profile after market sights. That would be different. Easier to see, but its not a USGI slide any more. My Union Switch and Single Company slide is.
M1911a1's are M1911a1's, don't loose any sleep if you think its "not all original" parts. Few are, and it doesn't matter. Get on your hands and knees and crawl through some rice paddy silk with it in your hand, shake of the big chunks and shoot it. It will shoot, and that's what counts.
