mustang engine

Hello everybody, I am not sure if I am at the right place with my question, but who knows.... Please may anybody advice me the best place (salvage yard, used parts selling company, web-site ...ect. (in the base of his previous good experiences) where I may find some usable complete Ford...

I have a 2000 mustang gt (auto) and I was curious on getting new cylinder heads, I know I have windsor heads because of the 13 bolts on the covers, but I don't know if its a 281/289/302/351. Would anyone happen to know?