Help with my first engine build (5.9 Magnum)

On used magnums the heads are prone to cracking. It is more common on the Magnum Heads. The reason is because Dodge went to a thinner casting in the cylinder heads from the factory. LA heads off any of your small blocks will have the same problem just not as common but, almost. They like to crack between the intake & exhaust valves.

Not trying to piss in your cornflakes or saying you need to buy need heads but just something to be wary of.