Is the block broken? You know there was two 53 blocks cast. A thin wall and Heavy cast. If you have over 100k on it I would not worry about it. I have one in my 98 12v that routinely gets driven hard and just installed a 53 in my 99 3500 that went across the dyno at 965 ft lbs torque and 522 hp. I built this engine three years ago. It is bored .040 over and has a stroker crank in it. If you are worried about the block you can check to see if it is a thick casting by removing the center soft plug on the passenger side of the engine and measure the water jacket thickness.The light cast blocks will measure .251 in the radius. Heavy cast blocks will measure from .270 -.405 depending on the year.