ST50GE timing/magneto

Hello to everybody
I'm pround owner of ST50GE which I have it since 1988 During my last modifications I mounted 90ccm cylinder and different sprockets. But... German bikes are very slow. As I discover original Magneto actually retard ignition to keep bike under 40km/h rule in Germany. I wish to change all unit but I have no experience which from ST70 will fit. I need 6V one or 12V but it force me to change all electrical system - not so big problem but always some extra work. I'm also looking for some second hand carb and inlet manifold for 70ccm engine as original one is smaller.
I welded my magneto and this helps much (higher reving) but I'm still looking for right and proper solution for her

To do away with the magneto fired ignition coil is not too much work. Use a conventional ignition coil with a live feed from a battery fed circuit and disconnect the magneto feed to the condenser. The black cable to the existing coil now becomes the low tension feed from the battery powered coil. This may get round any inbuilt restriction.