Just another update: stop looking for wheels and guards - got them! I also found a seat, but it is a) off an XL70 - slightly different shape - and b) totally turned to swiss cheese.... tried cleaning off al rust and attempted very carefully welding and brazing holes shut, but there just isn't enough metal left to make that work. So I decided to make a buck and some formtools and make a replica from flat steel instead. I think I can get it to match a good one I have on my first SL70K1, my current grandkids' bike. The rubber cushion of the XL seat will be able to be shaped to SL form and I'll sew a new seat cover in any case.....
Just about have all the bits for a K0 now. Lots of restoration work left to do: replating spokes and all bolts and nuts, hydroblasting all engine cases and some parts, checking all engine bits for wear etc. etc.
Frame is cleaned repaired and in for powder coating already.