The additional ground wire on the rectifier is your idea, Mark. From a post you wrote, maybe your thoughts ....
I had a roll of both grey 2.5mm2 and 4.0mm2 wire since the 80's...
Extra insurance
I remember having to do it once on a mega-custom 750 someone brought to me with 'electrical issues'. I might have posted something about it way back? He had the frame powdercoated and the ground cable was on the frame's outside, like so many are, and it melted a Green wire thru the main harness up to the coils where it bolted to the frame (site also not cleaned off). The screw there was spot-welded in place, a real bugger to get out! I think the starter did it?