I'd get 18" worth of pipe for the extension just in case. Better to have extra than not enough...I know the ext is more than 6" but its closer to 12"...maybe a little more.
As for the passenger hanger buy some type of generic hanger and make it work. I believe there is a piece of frame and a couple bolt holes that you could use to mount the hanger.
Good luck, let us know how it turns out.
