Re: 1970's Johnson gear shifter
It may be just the cable.Disconnect it at the engine . Does it move freelly now?.If so you may want to replace it. Perhaps take the shifter box apart and apply a few dabs of grease. With the cable disconnected from the engine does the engine shift easily? If not apply grease to the zirk fittings. Your shift/ throttle box appear to be in good shape for its age.A little corrosion showing that a good cleaning is needed. Work with it first. Unless you have lots of money then you may replace it.