My advice is this.

Use the link below to take you to the WheelHorse forum. Join and post your question there. Red Square is populated with members who work on Horses all the time. If you want accurate info quickly, then that's the place to go.

Here is a link that might be useful: red square

The main stacked pulley on the bottom of the crank-shaft has a bolt up inside of it that must be removed. Probably a standard 3/4 inch or larger headed bolt. Remove that bolt, and the stacked pulley should slide down and off. The indentation in the tube between the pulleys is what keeps it keyed to the crankshaft, to make it turn and move the tractor, etc. Once you get that stacked pulley off, some work with a sharp ice pick will get the old seal out, and after a bit of clean up, you can carefully tap the new seal into its place. But, if the crank-case seal is leaking, then you must take off the stack pulley, unhook any tubes, wires, etc., remove four engine mounting bolts, and remove the engine. After you get it out, and you have drained the oil and gasoline from the engine and carburetor, turn the engine onto its flywheel, and then locate and remove the bolts that hold the oil pan onto the engine. Remove the oil pan, clean it well, and lay it aside. then clean off any old gasket material from the block area. Before you install the new gasket, put a smooth layer of heavy grease around that area where the gasket goes. Then stick the gasket onto the block, making sure it is in the correct place. then lower the oil pan down onto the block, making sure that the governor shaft goes up into its little "boss" in the oil pan as you lower it into place. Then put in the bolts and tighten them up securely. Tight is "Tight"!
Install the engine, the oil, the fuel line, and if you didn't make any mistakes, it should start and run!
The first one i did took 4 hours. The next ones took 2.5 hours.