I second the above.. Don't start messing with replacing the cam, etc.. to something better in the hopes of getting more performance out of it. If (God forbid.. at this point, you've had enough bad luck) you should have a problem, I can see ATK saying they will NOT warranty the motor because you put after market parts on the short block that somehow, mysteriously caused piston number three or whatever BS they come up with to fail down the road due to your negligence.
I live near Washington, DC where there are more lawyers per square foot than probably anywhere else in the country. A local gentleman spent a very significant amount of money having his Porsche 911 restored by a very well known shop in our area. Everyone makes mistakes, and this shop is good about customer service in my experience, and does most everything in house. Anyway, the owner has his friend put new heat exhangers and a fancy new exhaust on this car to give it a bit more oomph, and the new exhaust is different enough that it comes a bit closer to the new factory oil cooler that the first shop had installed.
Well, the oil cooler ends up frying, and ruptures, causing a massive oil leak that destroys the engine, and darn near burns the car to the ground. Owner hires a lawyer when the shop tells him to get lost about warrantying the motor due to having had someone else work on the car. The oil cooler was probably defective, and a cogent argument could have been made that it would have eventually failed, yada yada.. The guy sued, lost in court, doesn't take the bus, but he's not driving that Porsche anymore either.
Bottom line was that he modified the car enough that the original engine house argued they didn't have to warranty it, even though they offered to put the EXACT exhaust, etc.. on the car, though their estimate was MUCH higher than what he got from someone else to do the job, that apparently did a great job putting everything together, but the oil cooler failed...
Check the clearances, do some other checks, put it together, drive the car, while you get the $$$ to do what you eventually want to do with the original motor.. This is an expensive hobby, and you have to pick two of the following three choices: cheap, fast, reliable.
Sorry for the novella
Billy