good luck, liz. it can totally be done, but most people opt not to because it takes a lot of time and welding abilities. my bf has a stock eagle II with the d motor that does 40 bone stock.
I have a foxi with a sachs engine, and its super easy to work on... but it'll always be slow. too hard to find a good pipe and clutch.
i also have a puch two speed, however, and youll be eating my dust.