Chev 88 350

88 Chev Truck 5.7 blowing white smoke out of tail pipes, milk shake look in oil, mechanics told me they could pin point "Exactly" what the problem is now saying they dont know say water in #7 cylinder, says could be cracked block cracked head blown head gasket. Truck starts great runs great lots of power. bubbles coming up from reserve tank also. This is my sons truck and we dont want to get taken any ideas suggestions would be appreciated to pin point if possible.

You mean they haven't given it a compression check to be sure? Probably head gasket but that would certainly isolate the problem area. Change the oil and see if it is still milky. Are you using coolant?
http://www.emotipad.com/newemoticons/Deep-Thinker.gif