Engine Help

I don't know I'm in the right spot or not but I thought somebody here may have some insight for me. I'm having a problem with a 454 out of a 91 boat. I spun a bearing a couple of years ago so I had the whole thing rebuilt. Everything was upgraded except for the crank. It has new connecting rods, domed pistons, world product heads, rollers rockers, cam and lifters. I told the builder I didn't want any problems and at the time money wasn't an issue. I've now had the engine out for the second time with the same problem. It breaks the lifter and snaps the rocker arm stud. Different cylinders and different side each time. Initially he said I over reved it, which in no way could have happened. The engine has ran about ten hours between the two rebuilds. He's scratching his head and I'm can't take another summer without my boat. He said he's check the tolerances over and over and has had other machine shops look at it with the same results. Someone said the cam may have been too big and a list of other answers ghat didn't make any sense. Has anyone heard of this problem? Please help! Thanks for your time, Mark.