What to look for in U-pull Magnum?

Yeah - they almost all have cracks. But they do not all get anywhere close to water. The way to properly test these heads is not to magnuflux - but to pressure test. Personally for me - I look for a running engine. I want to listen to it run, see it not smoke, hear it have good oil pressure and be responsive... Then pull the plugs and look at them. If they look good, pull it and don't sweat it. Taking them apart just leads to more pain and cost...lol.