If you are talking about your Squarebird, the Bendix gear is not electrical. These starters are called 'inertia' starters. They do not have solenoids that force the Bendix gear, either. Here's a site I made showing the entire starter... CLICK HERE
Regardless of polarity (how you hook up the battery), your starter motor will always rotate the same direction. (Don't believe it? Try it.) Why? Because in order to reverse a DC motor's direction, either the polarity of the field wires or the armature wires must be reversed. Since they are connected internally in a series, reversing the battery polarity reverses BOTH the field & armature wires. Reversing both effectively means there is no change in magnetism direction, which dictates rotation direction.
Whoever told you that pos or neg ground is better one way or the other doesn't understand the electrical operation.
A DC motor with permanent magnets will reverse direction because again, you are only changing the armature polarity, not the field. Only modern cars have permanent magnets in their starter motors.
Some folks have ran their classic cars for years, not realizing that the battery was connected in reverse. All Squarebird motors have no permanent magnets, not even the heater motor. The clock uses a solenoid 'clapper' to wind the mainspring, gauges use bi-metal (heat) strips to move the needles, and the generator is the same story as the starter motor.
So, do not fret over negative ground. 100% of modern cars use it. - Dave