The RC/RT series were sold as replacements and are probably best known as OEM for many Caterpillar Diesel 2 cylinder pony motors. Some 4 and 6 cylinder units were also made. They are very hot and troublefree with proper care. The pony motor mags came in many configurations, clockwise,anticlockwise, firing at 90 degrees, and 180 degrees.This means be carefull when swapping distributor caps. Some were gear driven, fortunately most were impulse coupled. Some were mounted horizontally and some even upside down.
If things are not complicated enough with combinations of all of the above, some had carbon brush rotors and others jump spark design. The jump spark distributors were equipped with a ventilated cap and/or housing as when the spark jumps to its proper plug post it creates its own private lightning storm. This private lightning storm reacts naturally occuring diatomic atmospheric oxygen O2(Means two molecules stuck together for non chemistry majors) into O3 or ozone. That is the fresh outdoorsy smell after a lightning storm. It reacts with atmospheric nitrogen (N2) and water vapour which makes HNO3 or nitric acid which is corrosive. Carbon brush distributors do not need ventilation but should be cleaned of carbon dust about every year with a brake or electric motor cleaner and a soft brush to prevent shorts. Be sure the cap is completely dry before reassembly and use because many cleaners are explosive and may cost you a new cap made of unobtainium or very expensive. it is also helpfull ro clean out air vents in the housing and cap in case muddaubers have taken up residence. Be mindful of the position of the mag when in service as the air vents should point downward when replaced to keep mositure out.
This example has a brush type distributor and plates on the side of the housing where vent covers would be if it were a jump spark design.
Points are set at .020. If you take one off a tractor or find one it is a good idea to take it apart, wash the bearings and relube with an electric motor grease or a black molybdenum product. Most studies show modern petroleum base grease will last up to 30 years with proper storage. Most of the iron we yard out of the boondocks has been sitting for far longer and not properly stored to say the least. Dab some grease on the cam the size of a match head while you are at it. If the cam has any rust, give it a good polish with some crocus cloth and a straight edge. The screws that fasten the points spring are a metric size, but standard. New springs can be made of readily available blue tempered spring steel.
Always check the condenser for leakage. If no leakage them check capacity, it should come in at about 0.2MFD. If it is one of the left hand 180 degree gear driven mags for a D2 or D4 beware of loose bearings in the engine, this will break the magneto shaft every time due to excessive radial force from loose engine bearings. Expensive lesson!
Here is a parts list from a factory service manual to help keep your mag in top shape. The grounding switch stud is often broken off. For safety's sake replace it if so. Use a brass screw and a stainless steel nut. Make sure that the wire from the stud connecting to the stop switch is sound.