Thanks to another forum I was able to identify my shifting issue on my new-to-me 74 550K rather quickly.
As suspected, the shift spindle spring (Honda part 24641-292-000) is MIA. Dealers are unable to provide because the part has been discontinued.
Does anyone have a source for this spring?
I could find a suitable spring from McMaster or Sears hardware if I had one to measure/compare. Not sure I'll be able to guess the length/strength correctly.
Thanks for your help.