Replacing Jockey Wheels
I need to replace the jockey wheels (derailleur pulleys) on my old Shimano 600 Ultegra derailleur.
Can I use any modern type of jockey wheel, or one made specifically for older derailleurs?
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.