Bolens 800 Transmisson Repair

I have a Bolens Husky 800 tractor with a 3 speed transmission. The input shaft to the transmission needs to be replaceed. The keyway in the shaft has become worn down probably due to the jarring from plowing snow. I have tried a new key but it eventually slips. The tractor moves, stops, then moves again.
My question is how hard is it to replace the input shaft? I consider myself fairly good in mechanical aptitude. Do I need special tools? Would it be better to find a repair shop? Just wondering what I might be getting into. I have the Bolens manual but it only talks about putting the transmission together not disassembly.
Any advice would be appreciated.
Thank you
Dave
St. Joseph, Michigan