Hooray, I guessed one right. I've only seen three 351W's torn down and they all had brownish black burnt looking rough scratched up main bearings. I destroyed a stock one when one of the rods went and after inspection, I deemed the whole rod assembly as wimpy. The rest of the rod bearings were o.k. so I assumed the bolt let go, but who knows.
bnicknel, the rods are very weak stock on the 351W. I have a theory on 351W mains, let me lnow what you think. Due to the larger main journals, they hold more heat and do not like high r.p.m.'s (over 6,000 on a regular basis).
not sure about the heat buildup but there is a lot more friction because of the larger mains however i've never had a crank fail, have had a a few rods fail though. only one on the windsors though. had 2 fail at the same time on the clevie.