Went to the shed for a look at my 28 and 29 600s and yes I have fitted side stands on the engine tube just behind the foot board. Not sure where they originated from. Could be Ariel Bsa or Norton or even Japan bike. It involves welding the hinged section to the engine tube. I notice I dont even have the rear stand any more but just a 1/2 by 1/8 mudguard stay.