Just tossing this out there as I am not familiar with aluminum heads on a big block, but I have had issues on smaller engines with the head warping. Happened 3 times in 75K miles on a 1.7 Volkswagen engine (actually still have the engine). Got to the point when I could do that job with my eyes closed. Had the head milled each time - finally put a 165 degree thermostat in and wired the electric fan to run anytime the ignition was on. Keeping the aluminum cool seemed to be the key.
Krister
Aluminum is not as sturdy a iron when it's subjected to overheating. The heads will warp, but if you get an iron head too hot it may crack. A cracked iron head is a boat anchor, whereas a warped aluminum head can be repaired. The newest technology uses an oven to heat the heads while they are clamped to a table to relieve the stress & warpage in the aluminum. They only have to surface about .004" to get them straight after this procedure.
BL
