I had to grind/sand the opening in the block to get mine to fit, not a lot, just enough to get the casting "flash" area to be the same height as the surrounding area of the starter opening. Let me see if I have a picture....yeah - here you go. I don't think the starter pocket is a precision tolerance machining operation. It must be just casting differences, this 66 440 block needed clearancing, the 73 440 block in my car did not.