Toyota Repair: Water in my oil after overheating, cylinder head gasket, timing chain cover

Question
I have a 92 Toyota pickup 22RE; The engine over heated and got warm a number of times, at least 3 in a 2 month period of time. I changed the radiator and everything seemed to be fine, for about 2 weeks.  Then one night while I was driving the engine started running rough and it died. Until that point the engine was cool and running fine. Needless to say I checked the oil and it looked like chocolate milk, I assumed that I had blown my head gasket. Now I am in the process of rebuilding the top-end of the engine. My question is when this engine over heats and the oil/water mixture happens where other than the head gasket can these happen? I'm planning on checking around the water pump and the checking the valve seats. Looking at the cylinder head gasket I cannot see anything that looks too bad. Are there other places, seals, which can cause the oil and water to mix if they are broken/ruptured due to overheating? Is it likely that the block could be cracked in some spot that I am not seeing? I'm kicking myself for not at least compression testing the cylinders before taking the engine apart, where should I go next? I still have to take off the Timing chain cover and chain but after that I'm stumped. I'm almost ready to take everything in to a service garage. The # 2 and 3 cylinders are clean and the 1 and 4 are normal looking so what ever happened happened in that area.

Answer
The block is the last place to be concerned about, if there is no obvious damage to the head gasket there are several conditions that can cause the coolant to enter the #2+3 cylinders.
The head may be warped but again, there should be some sign of headgasket leakage between the two cylinders, I have seen lots of these heads crack in the intake ports due to overheating, I recommend that you take the head to a qualified machine shop and have it pressure tested and if it is useable have them grind the valves and resufraced.

Another common problem area is the timing chain cover, if the timing chain is worn to the extend that it can rub on the inside of the cover it will eventually rub through into the water jacket of the cover, so I would actually remove the timing cover first and check for this, you will find the problem either there or in the cylinder head.
I still think it's the head because only two cylinders are affected if it was the chain cover there would be no difference, the cylinders and pistons would all look normal.  Hope this helps and good luck.