A few random thoughts... Magnum heads crack, never seen or heard of one that went into a cooling jacket. The aftermarket heads are to address other things - fitment and upgrade costs mostly. Johnny's right in saying it's a waste to use a brand new iron head combo. Personally I've never run a roller cam in my own engines, and seldom in customers', and there's no reason aside from a racing application where I'd consider it. Especially a hydraulic roller. That's on par with the waste of money on a new iron head IMO. That being said - when you can't control the cam break in and have to warranty the engine, it makes sense only for the builder - not the guy paying the bill.