Did you pull the wire when it was cold? I don't have much experience with a flathead since I got my car with a fresh engine. I do however have a lot of experience rebuilding Jeep 4.0 engines (as a hobby) and what you're describing sounds exactly like a worn out 4.0. With these jeep engines, the clatter (almost like a diesel) is piston slap. My daughters jeep was doing exactly what you're describing and when I rebuilt her engine there was one piston that I could make that noise with my finger rocking the piston in the bore. If left unattended too long, a piston skirt will break and not long after the piston ends up in the pan and the wrist pin commences to open up the coolant jacket. I've seen each of these stages during these builds. My daughters engine ran fine, the clatter stopped when warmed up, bearings and wrist pin were in great condition. I caught it in time. A bad rod bearing presents itself in a different way than what you're explaining. Not sure about wrist pins in a flathead. Jeeps are pressed into the rod and float on the piston.
