I think there are several ways to crutch a production block to get it to survive a high power level, at least for a while. A lot of tricks can be tried on a stock block for the money an aftermarket block costs. You just can't really get the nice big bore that an aftermarket block offers.
Malex just found some cracks in his race engine, after several years of low 10 second power. I think he was planning on an aftermarket block.......but ran across another stocker, and gonna build that.
(Oops, just realized I am on A-bodies. Malex's thread is on B-bodies, he runs a 64 belvedere)