[GT40FIED]

If the block is cracked the symptoms are a lot like a blown gasket, excepta compression test will usually reveal one cylinder way low (this can happen with a gasket too, but not usually). You'll sometimes find coolant in the oil if the crack is near a water jacket or a good sized split. Trust me...it's generally not a pretty sight. The engine that came with my car (a stock 302) was on it's last leg and after a few small mods and some hard charging, I literally ventilated the block when one of the rods decided it didn't like the way I was treating it (turned out it was a shoddy rebuild done years ago that the guy who owned it before me, the second owner, didn't know about). A huge mess of oil and coolant. Once a block is cracked, even a small crack, it needs to be replaced as many others have pointed out. You still haven't mentioned what makes you think your block is shot.