Hi Ken,
I did manage it in the end and removed the exhaust valve and spring in order to get to "that" nut. Easier to remove than to replace it I guess. You can hardly get your finger in there let alone a spanner. The C shape official wrench will not move the nut any distance to get to the next flat.
I have got the split type spring covers, but no advantage there, unless perhaps an extreemly thin spanner could be used that could swing into the coils of the spring for more rotation.
I did contemplate cutting the side off a socket and then welding a suitable handle onto it and I may well do that later. I am in the process of fitting the new barrels, so old cylinders had to come off.
In between this work, the sidecar frame is now all brazed up and being prepped for paint and the mudguard and stays completed. I will post more pictures on Flickr soon.
Mike.