The Mooney step-
The original Mooney M20 and all Mooneys from 1955 to 1964 had manual retractable landing gear (except the M20D with fixed gear) and a manually retractable boarding step that retracted by means of a crank located by the pilot's left leg and a cable and pulley system. In 1965 Moooney offered electric gear as an option on all new Mooneys and the emergency gear extension system went to the location of the manual step crank. For this reason they made the retractable step automatic and vacuum operated. It was made by Brittain, the same people that made the "PC" wing leveler system that also debuted in 1965 and all Mooneys from 1965 to 1968 had the vacuum retractable step regardless of electric gear, or manual Johnson Bar gear.
Mid way through the 1968 model year, the decision was made (under new Mitsubishi ownership) that the manual Johnson Bar retractable gear system be eliminated and the vacuum retractable step replaced with a fixed step. All Mooneys produced after this time either had the fixed step, or no step at all. It is relatively simple and easy to to remove the vacuum retractable step, or the fixed step and many owners have opted to do this over the years. So Mooneys may, or may not have a step and may, or may not have a retractable step.
If Mooneys could be operated as experiementals, I have always wanted to develop an electrically operated retractable step to replace the vacuum system. It would be pretty easy to do, but the whole STC process makes it not worth it. I also don't want to put the time and effort into it on hopes of a field approval.
I personally love my retractable step.