Yep,sounds very much like its a rod bearing- been there. Its common for Pontiac V8s.
DO NOT START IT AGAIN! A metallic sound means metal to metal contact, and every revolution means more damage. If you have a #s matching WQ HO motor, it is definitely worth rebuilding, and not too difficult. You can do the single rod bearing for less than $100, but while the motor is out, it's your opportunity to rebuild everything- then you'll get another 200k miles, if you're reasonably nice to it..!