Maybe I'm just lucky, but I have had no issues getting NR derailleurs to work with 5 and 6 speed freewheels with a 28T big cog. Didn't have to do anything special, it just worked fine.
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1964 JRJ (Bob Jackson), 1973 Wes Mason, 1974 Raleigh Gran Sport, 1986 Schwinn High Sierra, 2000ish Colian (Colin Laing), 2011 Dick Chafe, 2013 Velo Orange Pass Hunter