ACDelco 38001 Professional Idler Pulley

Is this idler steel or plastic?

What's the difference between the 38001 and 38006

will any of these idler pulleys work on my 1979 lincoln continnental mark 5 400 engine

Is this pulley a direct bolt on without having to add any spacers or make any type of mods. looking for exact fit. i am a ac delco person. thanks