Hey all! I just pulled my 1979 NA50 out of storage, where its been for the last year and a half. I stopped working on it in August of 2012...just prior to my divorce. The engine was soft-seized...but I went through and rebuilt it with some TLC. The last time I attempted to start it, it wouldn't...even though I replaced the ignition, etc. IF....IF I decide to replace the engine, which engines are 1:1 drop-ins? Will the engine from the NC50 work? Or the newer 2-speed one from the NU-50 (I think that's the model)?