i think the difference is the two inner bearings have different od's. the inner holes in the block are smaller. the id's are all the same on the bearings. this is in the older ones at some point they started to use all the same size. i have installed both i think the bigger ones or outside ones can be driven into the inner ones but it can cause cam binding. i think there is .010" difference of something. the cam should be same but you have to get bearings for the block. i think there are only the two variations for those engines. good luck and hope i haven't steered you wrong. hr