All the bushings in the front end will be getting worn out. Shocks like mentioned. The engine needs a complete overhaul unless already done including water pump bearings and seal. Good chance the water pump shaft is badly worn where the oil pump drives. Water pump belt when in there. Lower chance case bolt, I have had a couple break, and some come loose.
I have never had a big block polaris go much past 6000 miles on a crank. Usually by 5000 miles its time for a crank. Usually they failed and took a cylinder out with them.
The stainless exhaust valves on the 800 I hear came on some 2004's and all the 2005's. I cant confirm this but when you pull them if they are stainless there will be some fairly deep cut outs on the bottom of the valve to reduce the weight. The non stainless I'm told do not have that. Also when cleaning them you will not nick the stainless with a razor blade, the aluminum ones you will for sure nick or peel a piece off.
But honestly they are great sleds, I never really did any repairs outside of the motor until 7000-10000 miles on the sleds. And it was wear items at that point. Lots of sliders, carbides, bearings as expected through all the years. I changed some carb slides on one at over 8000 miles to stock the rattle. It still worked fine but annoying. My 700 and 800 lived their entire lives with a slp single, slp head.