Ok, my first 351. Stock 95 motor. Heads, cam, Intake, turbo. Made 530 ish, lost back to back head gaskets and then spun a rod.
Next. 408. Based on a 96 block. Lasted awhile, made low 600, chunked a piston. Replaced pistions, made 665rwhp, lasted a little while, chunked a pistion. Rebuilt. Sold car
Both engines, the block was fine, was never an issue in breaking. I hear the block is good to 1000 FWHP if you keep the RPM in check. I was never personaly going to go over 700 RWHP with mine.