I see that no one has answered, probably due to the rarity of that engine.
I believe that modern porting software and techniques could assist such an old engine. However I am not in the know with regard to that engine. From what I have read, Maico did a good job in providing a wide torque curve without a powervalve.
I ran a 490 Yamaha 20 years ago, lets see if I can remember what the specs were. I believe the exhaust port duration was 194+ degrees, the transfer duration was near 134 and exhaust port width was set at 68% of bore width. In addition, the exhaust port had the classic bread loaf shape that worked so well to allow enough port time*area while still maintaining piston and ring support. I remember it to be a upper midrange monster.
Chris