You're saying the starter sprocket (the big one on the crank) just spins, without the engine turning over?
If that's correct, you need to clean/rebuild the starter clutch.
Quick and dirty fix: Remove the chain. Find the little pin in the starter clutch hub (it looks like a zerk, but isn't) and remove it. Put some solvent (toluene, acetone, gasoline) in there, put the pin back in, turn it by hand back and forth. With luck, the solvent will soften up whatever's in there, and the clutch will start to work. If that works, drain the solvent out, and put a little light oil in there, and button it up.
If it doesn't work, you'll need to remove the starter clutch and open it up to give it a proper cleaning. Depending on the level of wear, you might end up needing to replace some (or all) of the clutch rollers. But try the easy fix first.
I was thinking the same thing but wasnt gonna say it because everything I say seems to be wrong but that looks exactly what my 72 or 73ish looks like.
You would think its the same tractor.
See what I mean? Thats far from a 50-some model