Join Date: May 2004
Location: Wilmington, DE
Bikes: 2016 Hong Fu FM-079-F, 1984 Trek 660, 2003 Specialized Hardrock, 2004 LOOK KG386i (RIP), 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1, 2016 Islabikes Beinn 20 (son's)
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The derailler pulley cages have definitely changed over the years but that doesn't mean that new jockey wheels won't work. It may be hit or miss though. Your best bet would be to try something meant for an 8 speed derailler. The cage spacing would be closer to your 600 derailler than a pulley for a 10 speed derailler. I just measured an old 7 speed 105 cage and found the width to be 10.3mm whereas my 10 speed Ultegra cage measured 9.5mm.
Note that you may be able to swap the bearings and spacers from your old pulley to new one. I've never tried it though.