Small Engines (Lawn Mowers, etc.): transaxle input shaft

Question
I have a 1999 John Deere GT 235 with a Tuff Torq K71 transaxle.  The transaxle input shaft is driven by a splined pulley.  The splines on the pulley and shaft are worn out.  Can I drill through the pulley and shaft and drive a roll pin through them?  Can I weld them together?  Is replacing the input shaft something a reasonably mechanical guy can do at home?  I've looked at an exploded diagram and it looks straightforward, but I don't know what might fall out of place when I split the case to remove the retaining pin.

Answer
You can weld the pulley on the shaft however this will ruin any chances of disassemby in the future.  The biggest challenge when disassembling this unit is resealing it properly and getting the "piston and spring" cluster compressed.  It can be done it just takes paitence You are already on the right track by having the diagram.