I don't know how to paste a photo or pdf into this page. However if you google:
curt dimberg rc airplane magazine
You will see an article from Aero Modeller magazine.
Curt just let me know that he and Ed Kazmirski collaborated in order to explore new airfoils, in order to facilitate aerobatic flying. The Clark Y airfoil is a flat bottomed airfoil, very efficient for level flite. He recalls that they aimed for a wing that was 60% efficient in 'normal flight' and 40% efficent in 'upside- down' flight.

He said that the FAA rules limited the engine size to .60 cubic centimeters of displacement, which limited the horsepower output. So they would purchase 5 gallons of methane and a small quantity of nitroglycerine, which they would mix at the field before a competition.

They also had an extra engine, because they would occasionally blow up in the midst of a competition.

He said that they kept the clearances between the piston and cylinder wall as tight as possible, by lapping the surfaces very gradually, running the engine up and down it's rev range, then examining the surfaces for wear patterns, then lapping those areas, over and over again.....