I think if it has the upswept pipe it will have originated as the enduro version.
Mine didn't smoke this much
Sorry I can't help you with dating/identifying the bike from the frame number, but maybe somebody else can help
The Rickman Enduro ISDE version was mine - a great little bike.
If yours is the MX version I guess it will be one of these :
https://motocrossactionmag.com/classic-motocross-iron-1971-rickman-zundapp-125-metisse/
Found these photo's in my photo reference collection, but can't recall any details about them.
Plus a photo of my ex Army ISDT Rickman Zundapp Enduro - a little belter it was
Being quite tall, I always thought the handlebars on my Majesty were too far back. so I cut the bar clamps off the top yoke and machined and welded them back on inline with the fork legs, and it steered a lot better