I’m mostly into pre-war motors, don’t know anything about the motor you have, but had a Mercury Super 10 that developed a bottom cylinder miss similar to what you have described. After completely changing the ignition from a Bendix to a Phelon, at a considerable expense, I found the problem was actually the lower crank shaft seal.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.