Hi,
Your 66 hand crank will work nicely. Originally, your 128 was kneebar operated so the side compartment probably only contains the controller. You can tell by the hole in the side of case. The controller can be removed to create an empty compartment though. I'm all for converting the 3/4 sized Singer with shot wiring into handcranks as it seems there more needed/ useful like this than as another electric sewing machine. (IMHO)
Jon