Anyone know anything about flathead 6 engines?

Like Aussie and Chief said, probably a rod bearing. Contact Egge Machine or possible your local NAPA store for parts. Hopefully you can drop the pan and replace the bearings and make it happy again. If the crank is a bit rough, some emery cloth can polish the nastys off and a .001 or .002 under bearing can be installed so the oil clearances come out right. It's not a textbook fix but good for breathing a little life into a old engine. Keep us posted. toolman