Many late-model fomocos still specify atf for the steering pump (trucks, vans) so I don't think running atf would be a problem. Seems like the vehicles that use a box as opposed to a rack spec the atf, and rack cars use power steering fluid.
Amusing note: the II specified "power steering fluid" (with a seperate part number) in the owner's manual, but the actual product spec no. was the same as atf.
I'd use atf, since the rack already is using it.