I put together my notes and pictures on converting old snowblower Tecumseh motors to minibike format. Lots of pictures (like 80 of them!) I'm sure there are some errors (will correct as I find them), but for the most part I believe the document is pretty complete.
http://www.pinrepair.com/minibikes/tecumsehmb.htm
http://www.pinrepair.com/minibikes/tecumsehmb.htm