When I sent my heads in for a core, which weren't the earlier casting because I replaced the heads before, they were cracked in between the valves. Thats what milzy told me.

Sounds possible if there was alot of detonation in the cylinder for some reason. But I don't see any other reason that it would crack.

It's not very uncommon to have cracking between the valves..
I could probably find examples if clubgp's search was better.

Still sounds like some overheating issues. Cast iron heads are very difficult to crack, even between the valves. The last several heads I've pulled that were cast iron were not cracked at all, even between the valves. And that includes many different sizes. Even on my '71 with 150k miles on it, no cracks. My '93 Bonneville with 220k miles on it, no cracks.

Now, don't get me wrong, in a general sense, it may be easy to crack the heads between the valves. Just one mistake as far as cooling is concerned (low coolant, driving on a dead water pump, plugged radiator) or running for a while with KR (most likely to cause cracking around the valve), and you have cracked your heads between the valves.