Tammi, The 'new' one is the correct motor how ever as long as it works it is no big deal - you are right the other one is off a Singer 500. I just had to go check mine. I thought well, maybe the bobbin winder runs off the shaft but it runs off the balance wheel so no reason to be like the Singer 500.
Joe, the Singer 401G and the Singer 411G are sort of a different beast from the Singer 401A.