AW4 from a Cherokee, but you gotta run a computer for it to shift. Also need to be sure if your engine is externally balanced (I think al amc V-8’s are externally balanced) as the 4.0 is internally balanced. This will require a custom balanced flexplate.
I would imagine finding an AW4 would be much easier than a 999 or 727. AW4 has an extra gear and is stronger than the 999 and equal to the 727.