The Rickman Zundapp and Montesa Micro Metisse frames have very little in common with the pre 70 legal MK4 Metisse and the pre 65 MK3, 3a and Petite frames are different again. I questioned Dave Tanner as to whether a Mk4 Metisse from 1968 would be legal under the new pre 65 frame interpretation and he replied with a definite NO. So, if the similar to a Mk3, Mk 4 is a no-no, the very different Rickman Zundapp and Montesa Micro's would be a definite no-no too.
Trust me Freaky, if I could get my Maico squarie powered Micro Metisse into my beloved pre 70 class I'd be bloody well doing it because I have a sneaking feeling that it's going to be a ripper of a bike. Unfortunately as the current rules stand, I'm building it purely as a Classic Dirt/HBBB fun bike and occasional pre 75 racer.