It means the blocks are the same design but I'm sure the Cosworth blocks where hand picked based on the bore tolerance after machining.
From memory I think if you look by the distributor there are four numbers stamped in the block. These dictate the class of the bore after it was machined, think there were 4 classes in total. I'm sure the blocks for Cosworth engines only used class 1 or 2 bores but I maybe wrong.
If your having the block re-bored anyway then it shouldn't be a problem.