That engine is not a reversable type and can only be reversed with a reverse timed crankshaft which is unlikely avalible for it.

Therefore you cannot run Counter rotating engines (one in reverse). This means you must use the same propellor on both sides and both must be facing in the normal forward orientation.

The direct answer to your question is I would use use APC 11x7 two bladed props on both sides. In addition I would avoid three blade props simply because there are only a few sizes avalible and thats a bad place to be with no choices.

I do happen to have that engine on one of my airplanes (Schneider Sport) and the 11x7 two blade is ideal.

John