I hear you on that, I've had more than one block stitch repaired with no problems so far, same thing on a bunch of 906 heads I had a industrial 413 block machined to 426 standard bore for my old M.W. NHRA stocker, it had a split cylinder(#3) in it and a matching external crack by the motor mount boses on the driver side that the machine shop didn't find when they, supposidlily, hot tanked and magged that block
If you think about the pressures needed to expand the block or heads far enough to crack them how much pressure is there on the non crack surface opposite of the cracks