The trigger group, stock or any other parts that do not fit the expected time frame, IMHO does not, in itself, indicate a arsenal rebuild. It could simply be parts changed out by a company armorer during the rifles service life or even by a former owner. Who can say.
Now if the barrel is not original, and I would agree with Latigo 1, that it is suspect, then one would be lead to think arsenal rebuild or at least a 5th echelon military repair facility. But then again, a former owner could also have switched out a barrel. Why, maybe a shot out barrel, a barrel with import markings, just a WW2 barrel that was better than the one on it. Again, who really knows. Was it a "good buy", if it was not a "good buy" now, it will be down the road a bit, so don't be to concerned about the cost. Just enjoy it and shoot it.