Yeah Warp, that works. Bolt hex head needs to be 17 mm across the flats. Swingarm and engine mounts. Instead of welding it, you could just lock two nuts together.....
My castle nuts (and swingarm pivots) were not that tight to remove that they needed drifts... But I soaked 'em first in 50/50 ATF/acetone mix.
The two sockets I mentioned can easily be shaped BEFORE removing the castle nuts... try it and see.... Don't forget - the swingarm and engine mount castle nuts are different sizes and you need the TWO modified sockets.