Depending on what you want to do, that cab and bed will bolt up to earlier 70's F100's. You'll have an instantly upgraded suspension and drivetrain.
If you want lower, front clips from, Volare's, MustangII, Dakota's, and a few more will work. I've heard the Dakota is the best choice because it can handle the weight better. The others tend to be stressed.
I'm sure there are MII kits for it, and I think a guy still sells a Dakota kit also.
EDIT: Those kits may be for the 61-64 straight axles, but I'm sure they have something for the 65-66 too.