Engine Size
There is an old rule of thumb which says to divide the weight by 12 to find the engine size. It works pretty well for smaller planes and glow engines. For example, a 5 lb airplane needs a .40 and a 7 lb airplane needs a .58-.61 engine. Your plane at 26-28 pounds would need a 2.1-2.3 cu. in. engine.
But, this is glow so add some for running gas, then add some for a biplane which has tons more drag than a monoplane. A US 41 might do it, but you would be happier with a 50cc/3.2 cu. in. class engine.