Primary V-belt,​​ 42 532174883

Put the mower deck in the lowest position. (Blow all the accumulated grass out. I used my compressor air.) Pull the front anchor pins and pop the arms loose. Pull the anchor pin from the cutting level adjustment arm. And finally, pull the last two anchor pins to free the power deck.

Pull the power deck from under the tractor. Loosen the housing on the left side of the deck to make clearance for the new belt. Follow the diagram and put the belt on the correct pulley's.
Tighten the housing down again. (You may have to "spring" the keepers...upright, flexible pieces of thin metal next to the inside pulleys...to make room for the the new belt.)

Slide the deck back under the mower and line it up with the brackets and hanger rods. Put your new belt around the power pulley on the bottom of the engine. Reattached the front hangers and put your anchor pins in place. You may have to use a pry bar against the mower deck in order to stretch the belt a little. Attach the last anchor pins and use the lever to lift the deck. You are back in business.
p.s. While you have the deck out from under the tractor, you might as well sharpen the blades. I used my Dremel. Quick and easy.

Removed mower deck, cleaned and replaced belt.

New springs brought back good tension . Cut metal belt guards out

pulled deck out from under mower

The manual says to lower the drive belt over the electric clutch but I did not have enough slack in the belt to get it over the clutch. Spent needless time (on my back under the tractor) trying to get the belt off. Finally, took the electric clutch off and the belt came off and went back on with little effort. Manual should just tell you to take the clutch off to start with.

Removed deck and cleaned
Removed original idlers and mandrels
Cleaned mounting surfaces
Installed new idlers and mandrels
Installed new v belt
Re-installed deck
Connected v belt
Adjusted deck
Test drive worked great

1. Removed the mower deck by pulling cotter pins, and slid out from under the mower on a blanket.
2. Cleaned under the deck with a wire brush.
3. Removed the drive belt, which involved disconnecting the clutch wire harness and the clutch locator.
4. Replaced the drive belt, testing belt for free movement.
5. Replaced the mower deck, fitting the mower deck belt around the clutch pulley.
6. Tested the mower deck belt for free movement.
7. Reconnected the clutch wire harness and the clutch locator.
8. Started the mower to test both belts.

Replaced the blades and the belt.

1) Removed belt
2) Routed new belt on deck pulleys, then to clutch pulley. Used screwdriver to help get belt onto clutch pulley.
3) Started mower, moved onto yard and engaged drive pulley. Belt worked perfectly.