Cool article, makes sense a friend in California told me he raced a pre production 3 speed 501 sometime in 1969.
Could be... in winter 1968 Maico tested an 480ccm Prototype in Laubus-Eschbach....
In 1998 or so, i found one and a half 3-Speed transmission in a Maico-Dealer's stock in Leverkusen/Germany and bought ist.
It fits in the normal 4-speed case with the 4-speed shiftingplate. The gearwheels were much thicker than on the 4 speed trans and the shifting forks were also very rigid
I gave it later to a friend of mine who has a 501 .... Maybe i'll take some pictures of the parts when i'll see him again, unfortunately he is living 450 Km from me
In the same dealers stock i also found the 5-speed prototype transmission, that fits in a modified 4-speed case !
The Dealer has bought the whole Maico parts of the former Maico-Builder "Merkle". So there were much old NOS parts from the former Maico-Factory included
Unfortunately some 5-speed parts were missing/demaged and the case was lost.... But i still have it