The stovebolts are all close cousins - so the basic fitment is not surprising. Chevrolet went to alot of trouble to ensure that the parts counter didn't give a serviceman the wrong part (including bright yellow paint stripes). My curiosity is sparked - I will try to find out what is different - but rest assured something is different. You have the bearing shells - mark them and try swapping them between the caps. Is the dowel/stake in the same spot? Compare how the original and the replacement fit on the block. How the edges of the bearing shells meet when the different cap and bearing combinations are installed. The top and bottom bearing shells should run on the same surface area of the crank - they cannot be offset.
