Just focusing on your first two paragraphs; so a case of two identical guns to swap and interchange parts between to “cherry pick” the nicest bits to make one nice rifle and one slightly rougher one. I can’t see anything wrong with that. My first question before you feel any guilt is how do you know the gun is original in the first place?

The general rule I follow is if I know beyond doubt that something is in original condition, that is the way it will stay. Otherwise it’s fair game, because in the decades of previous ownership you don’t have a clue what “originality” is actually left that you’re beating yourself up trying to preserve.

Cheers
Greg