Here is a old review done by Peter Chinn with a K&B .61 Lee Custom with pump engine.
http://sceptreflight.net/Model%20Eng...tom%20.61.html
He did get the best results using a 11x7.5 and 12x6 size prop at the time.
I think for the Escapade a 11x7.5 to 11x8 size prop would do the trick or a 12x6 if you wanted more thrust. You just may have to try them all to see which prop works best with that engine and plane combination.
If anyone happens to have the old back issues they did magazine reviews for the K&B .61 in the March 1991 Model Airplane News, and in the November 1975 issue of MAN too.