1) Scale models are not intended to be "rockets". You'll need to ask about how well it flew. Try asking in the Scale forum. Maybe the original builder has comments about it. Are you building from a plan with a construction article? Don't be afraid to build the airplane dead-stock. Engines were usually selected for a reason. Just because the airplane is large doesn't mean you have to go to a "big" engine to make it fly properly. Many 1/4-scale airplanes will fly very nicely on a .61-.91 size engine. It's just that today's modelers think they have to go to 35-50cc engines on large airplanes, and then they get too much weight and vibration for the airframe.

The small engines on the wings were for show, and would cause very little change if one quit in the air. In fact, I'd bet the model will fly just fine without them.

The wing loading at the area and weight you mention will be about 26.5 ounces/sq. foot. Not bad. Similar to many advanced trainer types, and with the size, should make a nice-handling model. 13 pounds is not an unreasonable amount of weight for a ,61 to carry.