From 1917 it's probably a 66-1. When they were rebuilt they updated the pressure foot to a low shank.
Your machine also has a larger diameter bobbin winder wheel and tire. Probably did that so they could use the original bobbin winder and the smaller hand wheel.
I can't tell if it has a Singer motor or not, but Sew-Classics has the belt you need. Mine have belt number 193077 on them. I've found that belt has fit all my electric 66s. You can also check with your LSMG.
Joe