What you have is an AMF Roadmaster built bicycle that was made to the specifications of the department store that sold Hiawatha-brand bicycles. Hiawatha was not a manufacturer, there were a store brand. What amazes me is how AMF named this a "Silver Jet", a name Huffman used from 1962-1967. This bike is from that year range and it is a deluxe model.
I don't know if the tank works and your fenders are missing. The fenders should be easy to find and the overall condition of the bike is perfect. I'd say about $250-$300 after you find those fenders.