Hi RCloud, sorry for the delay.
I just took apart my Sigs, and found that the locking inserts are not the same. Similar, but the slot to go over the trigger pivot is slightly different in location and size.
Then I reread your question and realized you meant breech block. I am sorry, I do not have any old West German P226's with the folded slide to compare. The stainless milled slide on my P226 is quite obviously not going to be the same as on the old P220.
Sorry for the delay and lack of help :/
I would still strongly guess that they are not the same. The folks on Sigforum might have the answer though.