I wouldn't seek them out either, but since they're the only thing Walmart sold for YEARS, there's TONS of them out there, I agree on the quality and such though, the 2 bolt backplate engines are nicer than the 4 bolt ones though, the only gasket on those is for the carb, the rest are formed rubber O ring type seals.

Anyway, with oddy's altitude and keeping the current plane flying, putting the engine on a diet or getting a lighter/larger engine would be the best bet, I'm sure there's some weight to loose somewhere, I know my McCulloch 32 has some to loose but most of it's weight is in the crankshaft... Have ideas but the plane flies almost perfectly how it is