I've been using 134D as hydraulic fluid since I've owned my Golden Jubilee, but yesterday my Ford-New Holland dealer tried to convince me to put 80W-90 gear oil in there instead.
He showed me the book they always check before selling fluids to customers, and sure enough, in a table titled "OIL CAPACITIES CHART/PRE-1965 FORD TRACTORS" it says, for the NAA/Jubilee, "Rear Axle: 80W-90 or 134D. 9qt.; Transmission: 134D, 5qt.; Hydraulic: 80W-90, 8qt." None of the other tractors on that page and subesquent pages recommend anything other than 134D hydraulic fluid for the hydraulic reservoir.
He made me a copy of that page -- the page has a book or part number(?) 06650075 at the bottom left and the date "November 1994" at the bottom right.
I'm guessing it's a misprint, probably swapped the advice for Hydraulics and Transmission, but maybe I'm confused. Does it make sense to use 80W-90 as hydrualic fluid in an NAA?