In what model and year range Ford can I find a Saginaw power-steering pump?

Almost all 1980-1996 E-Series (Econoline) vans. Some diesel and E450 vans in the later years had different pumps because of hydroboost brakes, avoid those. Ideally you want match up one from a salvage yard 5.0, 4.9, 5.8, etc so you can get the brackets to match your 302/5.0, or whateve ryou have because a Saginaw won't bolt into the more common Ford pump bracket you probably have now.

70s and early 80s big and med size sedans