speedometer cable

Hi there. I was trying to remove my dash to repair a broken trip reset knob, and I hit a snag. It seems the threaded studs, where my speedo and tach cables attach to the back of the dash, are loose. So, when I try to loosen either cable, the stud just spins. Hence the cables are stuck (for now)...

I have a 86 R80 RT 47500 miles than is a noise sounds like a fiber bearing going out seems to be coming from the speedometer or tach but when I pull in the clutch it stops anyone have any ideas thanks