Blown Head Gasket or Cracked Block

OK...I need some instructions please.
My daughter came home with her 225 /6 64 Dart yesterday with it not running very well. When they left the house...it was running just fine. When we bought the car...we found the points had came loose causing it to run about the same as what it was doing yesterday. I checked the points yesterday and the points were just fine. Pulled the radiator cap off and found oil in the cooling system. Check the oil and it was right where it was before they left.
Pulled the plugs and they didnt look contaminated.
How would I check to see if its a blown head gasket of a cracked block? I dont want to just start pulling it apart and find it wasnt either one...

Thanks
Rick