My model 27 doesn't have a boss either. When things on the quilt project settle down I plan to make an adapter that doesn't require drilling for mounting a hand crank. There's an access hole on the end of the 27 right above where the motor boss would be on other machines. I think I can make something that hangs from that. If the 66s have a hole there then it would probably work on those machines too.
I know CD just bought a handcrank that is combined with the belt guard for a 27 or 28. I don't know if Singer made one for a 66 as well.
Rodney