I went through 2 stock blocks with a 13.5 to 1 406. One with filler and one without. I wasted alot of money in Machine work Before I ended up with a Dart block. Motor dyno'ed 609 hp at 6400 rpm and both stock blocks split the top of the cylinder between 6 and 8. The cracks went from the cylinders to the head bolt in the middle. I think it has alot to do with the deck being too thin as well as the cylinders being thin.
My dart block ran for 5 seasons and more than 400 passes and I only took that apart to stroke the motor.