Well, I think I found the source of the clunking noise. I was hoping it was the clutch but it wasn't. It's the front pulley. The crank had some gouges in it, I assume because someone had a loose chain pulley. I filed them smooth so my belt pulley would fit. When I fit the pulley it didn't feel loose. I think my choices are to pull the engine apart and get the shaft hard-chromed. Or just park it and look at it for the rest of my life. Would a speedy sleeve work on a tapered shaft?