The ama keeps and sells copies of a good fraction of what looks like every kit or plan ever made-
It's gotta be in their list somewhere..
http://www.modelaircraft.org/plansmain.asp

I looked at the list of 'A' and there are many aeronca champs, but none exactly 64 " ws on there. But at least there are some leads..
The list says where the plan came from, magazine or kit..

I'm thinking air trials..