Christy,
All of the Singer motors with the junction box built in to the bottom of the motor that I have rewired, have used SPT-2 insulation. It's a bit tedious to work it all in there, but that's the way Singer did it, so that's the way I do it.
I also use longer foot controller cords. I have a very tall work bench and set my cords so the controller sits flat on the floor with the machine on the bench. They run from 4' 6" to 5'. For the power cords I usually just stretch a length between my hands with my arms held straight out. That's about 6'.
Joe