Overheating, steering and shifting are all separate things and have NOTHING to do with each other.
First thing to do for any machine that's sit for that long is to go over the whole thing changing ALL the fluids and greasing everything. ALL fluids means engine oil, tranny, differentials, coolant, brake fluid... ALL!
There should be about 18 or 20 grease fittings on that machine too.
1) Overheating- Is the fan running? If not, it'll take about 30 minutes of running to get hot enough to overflow.
Is the radiator full and clear of mud?
You can test the fan by unplugging the wires from the switch in the radiator and shorting them together with the key on. If fan runs when shorted but is not kicking on itself, you probably need a fan switch in the radiator... $24 on ebay.Here's a link for a cheaper than Polaris new one:
2) Get all 4 wheels jacked up off the ground for testing. You can't really tell much about a machine or what needs fixed by riding it. Check/change fluids and inspect the old fluids CLOSELY to determine its condition and if it has any metal or water in it. If the clutches were stuck they probably need to be completely disassembled, cleaned, inspected and any worn parts replaced.
Wiggle and rotate the wheels to check wheel bearings, bushings, tie rods, ball joints etc.
3) Clutch cover- Lots of them on ebay for $40 and up including the inner and outer covers.