The 70 and the 80 cc were two of the original sizes of 3W engines. The 70 became the 78 and finally the 85cc. The 80 became the 100 and currently the 106. The common part is the crankcase of these engines. Very nice engines. I have a manual for the 80 if you need a copy. I doubt if it is a lot different than the 70 other than needing a slightly different prop. You could contact Aircraft International for additional information.
http://www.aircraftinternational.com/

EXCAP232