I am going to have to think about this more, and draw up a couple free body diagrams, and do a few hand calculations. I agree that the engine has more load on it under those conditions, and it makes sense from a loading and resistance standpoint. And at WOT the vacuum advance will not be in play because there would be near zero vacuum, so detonation would not come into play, but when the fuel and air is exploding, the piston is at TDC so the force of the explosion should be relatively even across the piston face, and get transmitted straight into the connecting rod and crack and main bearing since everything is directly in line. Now as you move away from TDC you will start to load everything differently since its no longer in a straight line.

The part that is bugging me the most is what the force is to break the hydrodynamic wedge of oil between the rod bearing and the crank. This should be dependant on clearances and on oil pressure. I would question if maybe your 63 Ford would have lived under the same condition if it had tighter clearances between the rod and crank, or if it had higher oil pressure. Granted it seems like gearing was an issue too, but its still rolling around in the back of my head.

Out of curiosity, Jim, did you replace the rod bearings or did the shop? Did the crank get replaced too, or re-surfaced? Did you actually have a rod knocking at 2500, and 4500 miles?

Sean