With that light a wingloading at that size an aircraft, you could just about put a couple of the weakest Weedeater 18cc on there and still fly "scale" for a WWI biplane.

You may want to consider also the shape and size of the "cowl" or engine nacelle to see what engine configuration might work best. If they are long and narrow, RIRE engines like the Ryobi 31 might work best. For short and broad noses, SISE would be better. If you plan on counter-rotating the two engines, you may want to look around for pusher prop availability for the sizes you may need for particular engines, as their selections are typically not very extensive.