Been offered some new old stock roadster tank and side panels which i would like to put on my Mk3 interstate, i know the LH panel fits over a frame spigot where as the earlier ones have two fixings at the top, will the earlier 850 panels fit the mk 3
Yes, but not perfectly. You will need the Dzus fastener for the frame gusset plate and the grommet to locate the rear. The bottom edge just hangs, this can be prevented by using some rubber on the battery tray. I have had this set up from the day I obtained my MK3.
I pop rivetted a small home made bracket to the bottom of the panel that drops behind the Z plate.
If you've not got the old panels to work from then here's a diagram for the MK 3...