The crank-arm should be about 5 inches, center-to-center, and describes a 10 inch circle while winding.
The threaded-sleeve should be at least 2-⅜" to 2-½" from the open end to the INSIDE face of the crank arm. Threading is standard Columbia female thread ( ¼-20 ?).
Not sure about the offset for the arm: the machine measures 3-⅜" + from the shoulder of the winding arbor ( where the threaded-sleeve "bottoms" ) to the outer edge of the motorboard moulding.
That would suggest to me a minimum off-set of 1" in the arm.
Plating not critical, but would prefer no heavy rust / deep pits...
What have you in your parts bins / junk boxes ?
Thanks !

Frank McMullen