Replaced drive belt on a cub with electric pto this weekend, saw several post on forums asking how to do this. Here is what I did, might help someone later.
Remove mower deck and belt. Raise front of mower. Pull spark plug. Put finger over hole, rotate engine clockwise and find compresion stroke. Verify piston is coming up by inserting screwdriver in hole and slightly rotate engine. Insert a small flexible rope into the cylinder, will take several feet of rope. Pull electrical plug to PTO apart. Go under mower and remove PTO bolt. The shoulder washer on mine did not come off the shaft as it was rusted on. Sprayed the end of the shaft with PB Blaster and let it sit a while. Took a hammer and screwdriver and tapped on the washer, PTO fell off. The PTO is heavy so don't be under it when working. Note how the PTO is lined up under the mower. You will see the drive pulley and belt, AND the 3 thick tangs around the pulley. Release tension on the belt and pull it off the rear drive pulley. Remove the 4 engine hold down bolts. The steering arms are in the way of the rear bolts. Turn wheels for access to bolt heads. Wrap arms around the engine, using the oil filter and the starter, lift the engine up and prop it on the frame. Remove belt from engine pulley and feed it out of mower frame. Place new belt on rear pulley, feed thru frame and run other end up thru the engine hole. Wrap belt around the engine pulley. Drop engine back into frame. Go under mower and guide pulley and belt into the hole using a pry bar. Replace the 4 engine bolts. Pull rope out of engine. Rotate engine anti-clockwise and find compression stroke. Insert rope as before. Clean rust off of engine shaft and bore of PTO. Be sure key is still in PTO! Rub grease or Neverseize on shaft. Install PTO. Run drive belt thru the tensioner pulleys. Pull rope out of engine and reinstall spark plug. Drop mower back down and install mower deck. Couple of notes; if doing this yourself, you will be doing a lot of laying under the mower and standing back up again. Wear safety glasses as grass, rust, dirt, PB Blaster will be falling into your eyes, mouth, and hair. Thanks to mownie in this forum for help with the rope. Don't get in a hurry. As you read, it takes a lot of steps to get this done. Also a good time to clean and lube up the mower deck.