T-Bird With Cracked Engine Block

Hello. I have a 1991 Ford Thunderbird with a rebuilt engine and transmission. One day as I was driving it, I noticed that as the car was sputtering when I would hit the gas pedal. I wasnt sure what this ment. I was just out to get gas. The sputtering was occuring before and after i got the gas. The sputtering went on and off on my way home. I parked the car in my driveway to let it cool down (perhaps I overheated it). About an hour later, I wanted to take it around the block just to make sure it was okay. When I tried to start it, there was no crank. It sounded like metal on metal. It was very loud and I was very worried because I thought this car had reached its end. The next day I brought my car over to my mechanic(who is very good but lately has dissapointed me) and he told me that the engine block had cracked. However, NOTHING leaked from under the car in my driveway. I had thought that when and engine block crackes, all of the oil come out of the bottom of the car. This did not happen. Can anyone tell me if my mechanic is right and what I should do. Also, I took a look under the Hood and noticed no cracks.