What is the use of the car? All out squeeze every ounce of power out of it everytime you drive it? How high you going to revv it? I would think over 7K to get there with a SBM. Depends on use and the Tune as to how long it will live, same as any engine. As said earlier, usually something else fails "Broken Piston from running lean, broke rod from same, Loss of oil etc will take out a part and everything else in its path when it comes unglued. I have been there with a 340. It wasn't the blocks fault. It was the parts inside that broke and ended up taking out the block at 7200RPM. Was the weirdest sound ever, like a glass jar with marbles getting shook up. The pan caught most of it. I did however find parts of the rods and piston in the Carb. After I put the new motor in, I found out the Mufflers caught some of the crap too, Chunks of Rod, Valve, block and piston was flying out the exhaust.