I got a C6 trans sitting out on side of the house, came out of a f-150 i think can i use it on my 289

 

If it's got the right bolt pattern, yes. It would have to have been from a 302 or 351W truck.

That said, I wouldn't put a C6 behind a 289. While strong, C6's are incredibly inefficient (something like 40% power loss, iirc). C4's are plenty common, and you won't lose as much power to the wheels.