Finally getting there...
Once painting of the cases was done, I put the crank and gear clusters back in the crankcase. Turning everything over, something I hadn't noticed originally was pitting in the teeth of one of the gears. It turned out I needed sixth drive gear (obviously unavailable from Suzuki now), but a search on eBay came up with a NOS one in Cyprus. With a delay on postage due to COVID-19, all I could do was wait.
The pitting is visible in this pic. The largest gear in the top cluster.