The plans for the Flea Fly and the Flea Fly+10 are available from the AMA Plans Service.
For the Flea Fly they have the versions that appeared in RCM&E and M.A.N., for the Flea Fly+10 from Midwest and M.A.N.
I had a Flea Fly+10 from the Midwest kit in the early seventies powered by an O.S. 20 and it flew great once it broke ground (grass and 2" wheels).
It really got better when I changed to an O.S. 25

I just got the plans for the Midwest version and will be building it some time after the first of the year, will again be using an O.S. 25. I think the Midwet version
was built like the M.A.N. plans but don't remember for sure.

Good Luck,

John T