The rod bolts might have been overtightened in the past, or they might not have had enough lubrication to prevent stripping, but WHY did you keep tightening bolts after the first one stripped? I think new bolts and nuts are available from one of the restoration parts dealers, but once new bolts have been fitted, you'll really need to do a check on the roundness of the big end of the rod. I would suspect all the bolts now, and replace every one. I've always checked bearing clearance with Plastigage or a small piece of shim stock rather than relying on some subjective measurement like snapping the rod from side to side. Whatever clearance the bearing manufacturer specifies for the new insert bearings should be the specification to shoot for.
Jerry
