Making power out of the 318

Magnum heads crack between the valves in the combustion chamber. For normal driving I wouldn't worry bout it but have no idea if it's a problem when your squeezing every last hp you can out of it
Are there any iron closed chamber heads for a 360? Affordable aluminium heads? I don't mean to hijacked the op but I've been trying to find a good Affordable set of heads for a 360.