Many of the parts are the same..engine, starter, carb...
But lots are different. Differential, rear axle, tank...
Just today I installed an after market exhaust originally intended for an ES onto my SX..fit perfectly.
Current toys..
1986 Honda 350X..trail bomb!
1985 Honda 250SX..my main mudder
1985 Honda 250ES..Back in Black Trike
Current non-trike toys:
1990 Honda TRX300FW
1995 Seadoo GTX
1998 Polaris Indy Lite 340(Nearly new looking)
1998 Polaris Touring 500
1998 Club Car (electric)
85's are same,86-7 swingarms and brakes and such are different. Starters are also different from 86 on.
My personal opinion on buying 3wheelers, If the price is right and you have storage room, GET IT!! You can always fix it, trade it or sell it on down the road.