Thanks for the replies. I bought this 4.1 291 block a few years ago as a standard bore only to find out it was .030 over when it arrived. I put it into storage without giving it a good look. I just started to hone it to a 4" bore and saw that it has 2 sleeves. Those cylinders test thinner. I doubt that they are Darton sleeves. They look like about .060 thick. This is just a spare block to be used as a last resort.