The Goldberg is too small for a 50cc class engine..It only has a 77" wingspan and the weight is already supposed to come in at 14lbs (as you all know you can take the high side of the weight estimate). IMO this thing needs to weigh 11.5 - 12lbs max for awesome 3D. I dont think you will acheive that with a gas motor (even the DA-50) b/c of the exhaust weight, electronic ignition weight, weight of battery pack to power electronic ignition. I would go with the saito 2.20