One BIG grip I have with Simplicity is that they use a sticker for the model and serial numbers for the tractor and if someone isn't nice and write it down and pass the manuals along things are more difficult. One thing you can do is go to the Simpletractor board and they have a cross-reference page there that may help. I used it for our 918 Allis and 1920H Agco.
Nope, Those first pics are part#s and the last pics are they Sunstrand hydro ID numbers. The tractor numbers are on a chrome backed decal, when you are sitting on the tractor it will be on the operators left hand side of the frame just below the PTO engagement lever just as Art Stiverson mentions. Its a big sticker about 1.5" tall by 4 " long. If its still there and hasn't been painted over it should be fairly easy to see.