If you download the parts manual from tractorsmart.com you will see pictures of both valves and see the difference.
Both valves have 2 hexagonal pieces screwed into the end opposite the control handle. On the 3 way one of the pieces is about half as long as the other. On the 4 way valve the 2 pieces are float detent valves and are equal length.
On a 4 way you can also feel the detent position when you push the lever all the way to the right. It feels just like the float position detent on the 'down' operation of the lever, a slight resistance and then you can push the lever a couple of inches more. Don't try it the first time with a big load in the bucket!
Bill Tolle