Got the 38-inch, 2-blade deck on the 322 this morning...new 108" belt fits on just right, tightens snugly. Put a different spring on the deck belt tension pulley, fired it up and went mowing. Woohoo! Gonna have to make one more adjustment to the deck lift arms, to make them identical to the ones on my 38-inch, 2-blade deck on my 212. Basically,simple extension plate on the rear of both deck lift arms...to put the rear of each arm about 2 inches higher than the deck attachment point. Right now it mows great but the belt is barely rubbing on the front top edge of the deck because of this difference in lift arm geometry. After it cools down, I'll pull the deck back off, remove the lift arms and trot down to the welder shop down the road.
Gotta make top lift arm seen below look like the second one where it anchors to the rear of the deck: