Schwinn Point Beach with Drum Brakes front & rear

if you want an in-frame engine, options are sprocket and chain on left side of wheel (or belt drive or cvt, depending which engine you get, but all amounting to the same thing - left side drive) or a shift kit, which retains the natural right side drive of a bicycle. with a belt secondary drive, you would have a sheave attached to your rear wheel, which the drum brake wouldnt be in the way of. it can be all one belt from engine to wheel if you have the right clutch setup, it can be belt primary and secondary if necessary, or it can be chain primary and belt secondary, i think. could be wrong about the chain primary and belt seconday, not sure, but either way, as long as a belt is driving the rear wheel, there is no need for a left side sprocket. a shift kit is a jackshaft that will have a small length of chain going from the engine to a jackshaft, then on the other side of the jackshaft, another chain going from the shaft to a freewheel that is installed on the bottom bracket. if you have a one piece crank, you will need bottom bracket adapters which are sold by the same company (sick bike parts) which sells the shift kits. the shift kit then allows the bicycle's gears to act as a drivetrain for the engine. these are your options for drivetrains with in-frame engines. another option is friction drive, which is where an engine is mounted above the rear wheel via a rack, and a roller on the engine moves the rear wheel. friction drive is also applicable to front wheel drive.