Thrown Rod.
It sounds like to me that the thrust bearings are shot. That would cause the crank to "walk" back and forth. It could also cause the noise you hear and possibly the sparks if its that bad that its hitting the block or Trans. Try grabbing your crank pulley and push and pull in and out of the engine with your hands. See if there is alot of play.
The Best V8 Stories One Small Block at Time
OP this Guy has what I'm talking about: http://www.jalopyjournal.com/forum/s...d.php?t=264839


