I went through similar circumstances myself about 3-4 years ago with a new 14-1 406 race motor for my 56 Chevy. The foundation of my setup was a World Products block which failed and had an obvious defect. The block cracked after 30 minutes of run time. Was pretty much told by Mitchell TFB!! No warranty. My sponsor suggested getting the block sonic tested which cost me another $100.00 but said it might reveal what caused the problem. Damn glad i did. It showed serious core shift in the block. Basically the metal in the bore that cracked was pretty much paper thin. Did some on line homework and word of mouth and found many people had run in to the same problem we had. We presented our evidence to Mitchell and they finally said there was an entire lot of defective blocks. I got a refund and got me a dart block. I know how you feel, and its not good. I stood in that same position 4 years ago. Fortunately for me i was able to resolve my problem with minimal costs.