Welcome to the Ford board.
You're gonna get told this sooner or later so I'll just be the first.
Get an owner's manual! It's chock full of useful info about lubing, adjusting, using and maintaining your tractor.
Available from this site, ebay and maybe Amazon.
Most people here are going to recommend that you use a generic HyTrans or UTF in both the tranny and rear end of your tractor.
Look at the label. It will say meets or exceeds Ford 134D specs.
It is rather thin - like about 40 wt. But guys have been running that stuff in their tractors for 10,000+ hours with good results.
Check Wal Mart, Fleet Farm, Tractor Supply, etc for it.
You will need about 8 gallons to change the fluid in both the tranny and rear end.
Use the same stuff in your power steering reservoir too if you have PS.
Fill level plugs are circled in red in the photo below.
DO NOT loosen the slotted screw marked by the arrow.