Which is better

If the magnum heads aren't cracked their good heads, but the problem is nearly all magnum heads you find are cracked. Even on good running low mileage engines that don't leak anything. 99% of the time the owner has no idea their cracked because they do it between the valves where no coolant is flowing.

BTW: the magnum block has 1 big advantage, it is already set up for a roller cam. It also has a disadvantage in you have to use magnum style heads and magnum valve train parts and their are a lot less choices than for an LA. If it needs new rings it's a good possibility it needs bored also. Most of the time by the time the rings are bad the cylinder walls are worn also