The coil substitution Seakaye posted will work on many magnetos that have flywheel magnets. If your magneto has a magnet rotor on the crankshaft, like in the diagram that the Buccaneer has posted, that coil substituting won’t fit. Mostly because of where the wires to the points, and ground, come out of that coil. There is no know substitute (to me anyway) that will work on that magneto having the magnet rotor.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.