A "parts" gun, if it is a product of Uncle Sam's Clean and Repair program is as valid a collector's item as one that is "factory correct." My 1st M1903 has a 1918 barrel in a 1918 receiver but a WWII "scant grip" stock.
I refer to Hatcher on the subject of Low Number M1903s, he found a few bad production runs but most of the Low Number M1903s were in service for years
with no problems, and the troops back then did a lot more shooting. IIRC Kraigwy said Low Numbers are barred from CMP matches if that is a consideration.