Now that this project is complete I feel I should post an update. I was just finally able to put my motor and new controller in. I did the 72v 5Kw BLDC VEC300 from Golden Motor and it's gone pretty good.
All that worrying about voltages probably didn't matter, because there was a drop down in the controller configuration for 48/60/72. Selecting 60v also set the upper and lower settings for amperages, etc.
I do have some questions about some of those settings, but I will start a new thread for that.
Thanks to all the folks that offered me help and advice all that time ago! :-)