...but in answer to your question, and perhaps someone here can confirm, but I don't "think" those old Bally's are polarized. So, aside from the ground, it shouldn't matter which wire connects where.
I did some research on this a while back when I got my Paragon. Realized the hot and common were reversed when compared to my other Bally's when some Led's I popped in didn't work. But, the game boots up and plays fine. No issues and all test points check out okay. I replace the power cords on all machines I buy. Generally with the older Bally's, I go with the original cord, but I'm a bit of a purist with that stuff. A more modern day cord will work as well. For home use, either is fine.
I can take a closer look when I get home from work tonight and let you know which wire goes where, normally.
Aaron