360 heads on a LA 318 vs Magnum heads on a LA 318

First time ive heard there is a difference between magnum heads.

As for identifying cracks in the heads. When i pulled the valves, i usually spray down the ports with brake or carb cleaner. I read somewhere to let them soak and then heat them up with a propane torch. The cleaner will boil out. On the first head i checked, the carb cleaner evaporated, but since the crack was still filled with cleaner, it left an identifiable line.

I was doing a head gasket on my brothers boat... 4 cylinder. I figured, lets clean up the ports with a grinder before sending them out to be milled. Sprayed them down...those were cracked.