Also, it could have been a slight mis-step made by the original builder. A lot of variables could be present. Even down to the way the engine block halves mate up. I've had a raised ridge show up that wouldn't let the intake manifold sit down flush, creating a taller profile under the hood. If that happens, I file the block down until the intake fits good. I've also had to work on motor mounts that had little ridges, or small amounts of flash that wouldn't let the engine sit as low as it should. These possibilities could be present in these previously built 'Bees. Probably not worth tearing the model down completely, especially if you can remedy the problem by filing the carbs and/or air cleaner. Let us know how it works out.