Stay at 331, and you say you broke a rod bearing, as in spun a bearing? If so, just cut crank, new bearings a balance and out it back in. The difference in a 331 and 347 you will never notice on the street and the side loading on the 347 on an already marginal stock block I wouls dtay away from, its up to you. Sounds like there is more damage than a spun bearing, but if not I will buy it, got pics?