The bolt is probably a J5, not J3 - in any case, you are right - a Springfield bolt from about mid-1918. Depending on how "deeply" checkered. it may be a 1930s buttplate which would definitely be a replacement.
"Technically" the serial number is one of the low numbered receivers, but was in the "gray area" that could have been double heat-treated. There was a couple of interesting threads on a rifle of Fred G's in the same serial range some time ago, if you can locate them. There is a possibility that your rifle could be substantially original. Any chance of pictures?
"We make men without chests and expect from them virtue and enterprise. We laugh at honor and are shocked to find traitors in our midst."
--C.S. Lewis