I recently had the SR indexing problem on my Mclean. I had a spare used NR headset to replace it, but chose to keep the upper SR parts and used the NR parts on the bottom. Worked out well enough and keeps the (mostly) SR group/look on the bike intact.
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1989 Schwinn Paramount OS
1980 Mclean/Silk Hope Sport Touring
1983 Bianchi pista
1976 Fuji Feather track
1979 raleigh track
"I've consulted my sources and I'm pretty sure your derailleur does not exist"