Diesel replacement engine

Howdy,
I have a 2003 Craftsman with a 6 speed manual trans. It has a 17.5 HP, OHV engine on it. It's torn apart right now (the valves need reseated). The engine looks really clean for its age and should run good once I get some valve grinding compound. However, I kinda want to put a diesel in it for fun. The stock engine is a vertical shaft and I don't want to go through the hassle of making it a horizontal shaft configuration. I need to find a cheap, vertical shaft diesel engine. Does anyone have any suggestions? Ideally something with a respectable number of horses.