1974 Hagen All Speed Crank. It's a 285% CVT, and because it's very thin, not a whole new hub, it may be possible to attach to a clam shell adapter or top hat adapter.
It is fixed i.e. not freewheeling.
It comes with the crank arm attached but doesn't appear to need it in any way to function. I'm not certain that the shifter thingy works on a tube that isn't radial to the axle, as a chain stay is tangential but then again it might be fine.. looks fine.
I wonder if you feel it pulsing.