I thought they were all basically the same, is there a difference in the motor mount setups for the cubs?
It may not have you specific model listed, but they probably do fit also.
I am sure that some minor wiring etc will need to be done. A 1964 honda is going to be a 6 volt system and the new motor will be 12 volt. Also the new motor will be a CDI ignition and the old a points ignition.
I googled trying to find a pic of a 64 cub and found this forum that might be of more help for you.
http://planetminitrails.com/webboard/
Please keep us informed here too. I am looking at repowered hondas too.
Allen