Well I have finally finished the LT1 swap for a friend. Get everything ready all fluids full and try to start the car and it fires right up, sounds good. Crack the throttle and there is the *** awful rod knock, I have let it run a total of 5 minutes and the knock is getting worse, only thing left to do is pull it back out and go throught it. I call the guy and tell him about it and come to find out he is at least the fifth owner of the engine since it has been pulled, and who knows how long it has been sitting. I wanted to go through it before we put it in but he wanted to "geter done" Oh well, more $$$ for me

 

Sounds like it may have spun a bearing, you may be able to get away with pulling the crank and putting new bearings in it.