[Irish1941]

You say they worked before you took the truck apart, then they will work after, right?
Belts retracted when you unclipped it from the female end?
Maybe somebody put earlier '76-'77 belts in it.
Pull the belt all the way out to where you see the tag. Tell me the part number on that tag and I'll tell you what yr those belts are.
78-90/91 belts all had plunger and yes it needs to be there to work properly.