Series 2 Radius arm removal

[lorawhite]

I have just attempted to remove the main securing bolt from the flexible chassis mount at the front of the Radius arms, the bolt turns (very tight) but is not undoing, is there a captured nut inside the inaccessible chassis box section behind the front seats, I can hear what appears to be a nut turning but it is not visible, I’m thinking the weld on the captured nut has failed.
Question is, the best way to access the nuts ??

[mgcjag]

Hi...the cup that the mount goes onto has a thick plate welded inside it that is threaded.......could be a stripped thread on bolt or plate.........you could grind off the bolt head...to remove radius arm.....Steve