The block will be ok, and as long as the engine has been maintained correctly, it should be ok as long as you don't push it. The main thing that'll probably give first would be the rings. The stock piston rings are not designed for boost at all. The stock pistons aren't too bad, but they aren't that great. The 11psi recommended is still a lot of power. It wouldn't hurt to invest in forged pistons and definitely good rings, then since you're in there might as well toss a 4.2 crank in there. Super Six Motorsports has a kit with the 4.2 crank, forged pistons, rings, and pins for $1500. They have a "Long Rod 4.3" that also has includes H-beam rods and ARP bolts, $1775 sp $275 extra for the rods and bolts.