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jet sanchEz If you’re looking for “period-ish correct” Suntour XC (not XC Sport or Pro or Comp or anything- just plain ol’ “XC.” That was the TOTL ATB group for 85/6.).
If you’re not worried about being sorta correct, but want excellent performance and still be “vintage;” the Suntour XC 3 pulley is about my favorite for wide range gearing. It shifts great, looks kooky-cool and it wraps more chain than anything.
If you want Shimano that’s “vintage,” but has great performance and has a touch more modern style (and SIS compatible) The “Deore” MT-60 and Deore DX MT-62 are excellent- as are the Deore XT M732 and M735. IMO- the 735 dominates this group.
If you don’t care about Shimano- the Suntour XC Pro and XC Comp are about as good as ATB rear derailleurs got for that time.
And if you want to throw stupid money at your bike- the Dura Ace 7803 is the finest “classic” looking RD ever.