[WAH]

Apology not called for, if I managed to remove the nut the bolt will remain seized with no simple method of pulling / drifting, my thinking was taking the head off will enable drifting toward exhaust through access hole in swingarm.
Whichever method proves fruitful it's going to get ugly, spoke with local machine shop and his view is the bolt is effectively "welded" in situ given zero movement.