Just take the crank to be measured at an engineering shop, as the polish or regrind is not expensive and will save you wasting money on shells if it is needed, Mine had not worn the bearings out but when checked was afew thou oval so had it ground -0.25 I think the crank grind only cost about £55, only a 3rd of the bearing costs, so wouldn't advise just changing them without checking first. And also my engine had only done 60k.