Many companies still offer heavy duty axle carriers with tapered or double row bearings which are strong and nicer than stock. I see ads for them in dirt wheels magazine every month. You don't need to replace the axle with the carrier but a new, stronger, wider axle would make your x handle real nice. Lot'sof exhaust systems still around too. DG makes a decent four stroke one for the x but see what x owners on this sit are running as I am all 2 stroke. Welcome aboard!
own:
1986 250R- ported polished, carb mods, Esr atc-5 pipe and silencer
1986 250R- mild porting, carb mods (Clean!)
1985 350X- all stock (super clean!!)
1985 350x- desert project in the works
1986 250sx- Mostly stock
1985 200x- (pretty clean mostly stock)
1985 Yamaha tri zinger 60