I have a 323 and used a Lewmar 1000 horizontal shaft, though you could use a 750 according to the specs. I was able to get a decent discount and figured the beefier 1000 would take some abuse and last longer. Does the 321 have a shelf in the anchor locker to mount a winch? I HAD NOT YET SEEN A FACTORY SETUP ON A 323, so had to research a little to make my choice. The desired angle of the rode to the windlass should be horizontal or (better) uphill from the roller to the gypsy. Helps grab the rode., though not so much important with rope rode since you can give it several wraps, but you need every bit of chain/gypsy engagement as possible. I mounted mine on a block to raise it as high as possible (and still be in the locker) to get a batter angle for the rode.