The old Elnas had the double insulation sign, a square within a square. At least the Supermatics I've seen all have had it. The plug probably had a simple cut out plate of sturdy carboard or a bit like mdf to cover the wires. I don't think you would gain much by adding a three pin earthed plug unless it was truly grounded some how? Plugging it into US 110V will result in a machine running very slowly if at all. I think this zigzag model has the rubber friction wheel, but you have to take off the hand wheel to check it. It is similar enough to a Supermatic to use the manual for it. It has slightly different thread guides, and I don't think yours have an Elnagraph (the cam mechanism) or any built in stitch patterns. You have the wrong bobbin for it, the
correct bobbins have holes on ones side and solid metal on the other, and they are sligthly curved. My Supermatic needs the bobbins with a groove inside the hub to go properly on the winder. On top of your machine there's a class 15 bobbin (holes on both sides). They are too tall for the bobbin case and will act up with the tension spring, the flat sides will make them turn less smoothly too. As a temporary replacement a class 66 bobbin will do for some test sewing.