Had a thought and re-positioned the numberplate, now sits on the top leg, bolted onto some brackets welded to the frame:
Been on standby today, so I thought I'd make use of my time waiting for a phone call by making a battery box. This is about the closest I'll ever get to being paid to build a motorcycle!
First attempt was going quite well, I made it from some quite thin sheet, so it was just one piece, which could be bent into the box shape. I folded it up the best I could, but to be honest, it looked pretty amateur, and I was not prepared to put it anywhere near the bike.
Second attempt used some 3mm sheet, so every side had to be cut to size before welding it together:
Bit of a tight fit for the battery, but at least it should't shake around.
Next up was to sort some mounts, so the battery box can be bolted to the frame and still be removable, I've got the bits cut and drilled, but can't weld it to the frame until the next time I've got the engine out. The idea is to have the battery fully supported, but without any obvious supports - all you will be able to see it a bit of 10mm bar, stretching across the chassis legs. pics to follow when its welded up.