I've come up with a solution, I've made a aluminium bracket that bolts onto the earlier engine cases and then has a hole drilled and tapped into it so the extra mounting lug can be used.
Here are a few pics of the bracket fitted in development:
Here are some close up pictures:


For anyone that has one of my mk2 cases or someone who has a later case fitted to an earlier bike this would be a great addition, especially if you have a 500 ;)
Bitte entschuldigen Sie meine mangelnde Deutsch, Ich bin kein Spammer
Danke,
Andy