Jodie,
Welcome to the Quilting Board ( as a new poster anyway )
I don't think that is a 41 vintage machine. It looks more like the more recent Indian made Singers. It is a Singer, not a clone, but not a vintage machine either.
Here is a link to the Indian Singers that look very similar to yours. {
http://www.singerindia.net/Straight_Stich.aspx?id=1 }
You can find service manuals on the Singer site {
http://www.parts.singerco.com/IPsvcManuals/ } but I don't know how close to yours these manuals will be.
To stop the needle bar from moving I'd remove the hand wheel, clean any and all old oil from the shaft and inside of the wheel, then put one drop of sewing machine oil on the shaft and put the wheel back on. That should free up the wheel when the stop motion knob is released.
Oh, when you remove the stop motion knob, make the clutch washer with a Sharpie so you get it back on the way it cam off. They can be turned 180° out and then sometimes they won't work.
Joe