It looks like an early Stingray, perhaps some other brand's knock off even. Those speedometers were a popular add-on in the mid-late sixties, as were the tall sissy bar on the back of the seat. No idea about a possible engine/moped, but there were accessories that looked like motor and tanks some put on these bikes. Mattel and Marx both had toy motors that also made sound effects.

Those forks look like a custom built springer and extension, never seen them before. Schwinn made a springer that was based on their older models' chromed single spring front forks on their full size bikes.

Someone that has in-depth knowledge of the various Stingray, Mantaray and Krate bicycles can give a better set of thoughts than I can offer.

Bill