I'm using the SynchroSpark on mine because I've been using the same ignition testing engines up to an 81cc Huskey. The 42 uses the same 8mm crank as the smaller engines so the C-H prop adapter should be fine. No carb adapter needed. I would think the 54 you're looking at would be worth that much as long as it has good compression. But Poulan replacement parts are resonably priced, I got a new cylinder, piston kit, and front seal for mine for $101. the 54 makes some serious power, here's a shot of mine with a 22x10 scimitar on it.