Years ago I was looking for a set of heads to use on a 360 I was building. I was condiering both LA and Magnum heads. I took 6 pair to the machinist, one pair at a time. I pulled 8 sets of heads at several wrecking yards trying to find a set that were good to use. In all but the last pair, there were at least ONE crack if not more. The Magnums crack between the valve seats. My machinist said that while the cracks aren't likely to hit the water, it makes more sense to keep looking for a solid pair. I finally found a set of LA '923 heads from a 360 in a truck.