Is it using coolant?
Where is this coolant going from the cracked heat or block?
Is the radiator getting filled with pressure?
I'm sure by now you have pulled the block drain plugs and flushed it real good haven't you? poked the holes with wire and dug around in them?
Does this truck overheat on the highway at a steady speed, or is it just idling around when it overheats?
Slow speed overheating is from lack of air flow, highway speeds is lack of coolant flow, in general, but not always.
The carburetor is not super lean is it?
You have the timing set close?, retarded can cause a lot heat.
Is the block bored out more then .060"? thin cylinder walls can cause extra heat.
I read that engines run on the dyno need the heater hoses hooked up and not capped off because the engines run hotter with them capped. Are yours open or looped together?
Hook a pressure gauge up to the radiator overflow tube and see if it climbs up over the cap pressure quick, thats a good sign of broken gasket or iron.
Joe
