You are on the right track. The APC 12.25x3.75 works well with it. I have friends using the engine with props from 11x4 to a C.F. 12.5x3.75 3 Blade repitched to 4.0~4.5 in a .60 size model.

The prop will depend on your model and weight. I like to setup the prop for the model more so then for the engine. For example I can put the Enya SS50 in a Vector and use a 10" prop, in a Pathfinder a 11~12 prop,  or for the SV-11 a 12~13  prop. 

The engine will develop a tremendous amount of power above 9700rpms and can be used in any .60 size model.

If you get into a 4-2-4 situation I recommend adding head shims or reduce the venturi to keep it in 2-2-2. Enya has head shims for the SS50 in two different thickness, the aluminum one is thicker and the copper one thinner.

This is one of the reasons I love the Enya brand, they have all this stuff to help us tune the engine, including several size venturies.

Martin

Enya has an optional  Reverse crank for it as well. JXF has a 12x5 reverse prop ( http://www.himodel.com/plane/JXF_12x5_inch_Beechwood_Propeller_Counter_Rotating.html) and Zinger has all sizes.

Martin

Enya has an optional  Reverse crank for it as well. JXF has a 12x5 reverse prop ( http://www.himodel.com/plane/JXF_12x5_inch_Beechwood_Propeller_Counter_Rotating.html) and Zinger has all sizes.

Martin

I did not know about reverse cranks being available from Enya. 
What other Enya c/l engines do you know of that also have the reverse crank available ?