AMF made, late 50's, that's my best guess. That sprocket was the one made just before the star sprocket was offered. Straight bar frame also suggests mid to late 50's. Looks like some one didn't realize the seat stem tightens like a handlebar stem and drilled a hole to hold it instead. The forks may be able to be bent back, but it's hard to say how strong they would be. Was the serial number on the rear left dropout or bottom bracket?
Nice bike though, I couldn't say if it had a tank or not.