[olddog]

I am not a subscriber to the theory that "$hit just happens."

It happens for a reason. Doing the same thing over and expecting a different result is one definition of insanity.

Since it sounds like you did things correctly, look hard for a problem, as suggested by others. Are deck and head surfaces flat? Is the head or block cracked? A 40 year old cast iron head cracking is a real possibility.

Many engine blocks have the head bolts threaded all the way into the water jackets. I have heard it argued both ways. Some say lube the bolts to get accurate torque. Others say use RTV to seal the water from flowing around the threads. I guess you can RTV studs and lube the nuts and satisfy both arguments. Any words of wisedome on this, by you more experianced ones?