I am struggling with removing the windows in my doors of a 65 ss. The fastener keeps spinning and I can not get my hands behind the window regulator to stop it from spinning. Any thoughts?

Welcome

Are there 2 screws holding the roller channel to the bottom of the window frame? I remove those and leave the regulator in. also, you will need to remove the window stops.
now, that is on a 61, I have not tried a 65.

If you get that window regulator in the right position, you will be able to get behind it. It requires some finesse and you will cut your arms on the sharp door openings, so take it easy!