Coolant in the engine oil

I have decided to help a friend with this car. He knows nothing about cars and I am just a guy with a high mechanical aptitude but I am no expert. I have always fixed my own vehicles and think I can help him. I will apologize in advance for the length of this question but I want whoever reads this to know exactly where I stand and what has been done. Let me first say this car has been severely neglected. My friend told me the mil or check engine light was on and he cannot register it because it will not pass a smog check. He wants to sell it and does not want to sell it that way either for obvious reasons. When I picked the car up to take to my place my friend told me that I will have to add coolant when I get it to my house because the water pump is bad. The car ran terribly and had an obvious misfire. I got it home and placed an obdII scanner on the car to check for malfunction codes. The codes were, P0106, P0171, P0193, P0191, P0300, P0301, P0302, P0420, P0122, and P0000, all of which were stored codes. I did my repairs after researching the proper various voltages and pressures and air flows and according to the manufacturers requirements. One problem I am having is that it is very hard to perform a complete drive cycle in a city of more than 2,000,000 residence in order to have all the monitors report to the computer. I live in Las Vegas and even at 3:00 am there are people driving on the freeways and surface streets. I have, however been able to repair most of the issues. Only two codes remain. A P0300 and P0000. Now, that all being said, I never noticed any leaking coolant and I have had to put some into the reservoir. With the random misfire code I have done just about everything I can think of except checking all the wiring for broken or un-insulated wires. Well, in doing so I had to remove the intake manifold again and all the hoses the go with it. That is when I noticed milky white oil at the PCV valve. I then, hoping not to but did find the engine oil the same way when I drained it. I know what this means but I want to ask, is there anything else that can cause coolant to get into the engine oil besides a blown head gasket? And I believe the fact that it would be low on coolant but never show signs of leaking should have been a clue to that had I had more knowledge. My friend bought the car with the check engine light on and he was hoping to get the money back he bought it for. I cannot believe he bought a car with that indicator light on but that is irrelevant now. Can it be anything other than a head gasket? Thank you for reading all of this.