I just replaced the shift cable on the 1981 Merctrans and trs. I have tried everywhere and can not find information on how to correctly adjust the cable. Who can help out please?

Using the center bolt that holds the arm on, the roll pin under it, and the lower bolt that mounts the L shaped bracket under that, should be all inline with each other for Neutral. There are no detente's to help.
Hope this helps, Einar

PS your lower pic shows the parts I'm talking about.