Almost imposible to find a non cracked magnum head. I have torn apart 100 cores to get 2 litterally. Most of the time I just look the other way as they don't cause issues, I just needed a pair to install bigger valves do a bunch of porting and felt I should start with a set that is not cracked. I have had the best luck with the early casting, never seen a later casting that was not cracked. If this web site did not get all screwed up a while a back I would post a pic of how to identify them still in the car. Even so it is 1 out of 5 of the early ones that had no cracks, most of the ones on my shelf evn the early ones have at least one crack, the later ones have both ends cracked most of the time. The crack many times more percentage wise than 906 heads, they just don't seem to ever cause an issue. A bigger issue I see as these engines age is the receding exhaust seat, try getting a machine shop to install new seats when there is cracks also.