Actually I used the lever on the side that used to raise and lower the blades for a brake by welding and rigging some linkages to the actuator that normally applies the brake.
(I learned that these things need brakes the hard way.) Usually on mowers the belts are the brakes. But when you swap the pulleys from front to back to gain speed they have a tendency to fly off. So, then you have no brakes at 25MPH. Not good.
I use a pistol grip shifter handle that looks like a revolver grip.
And the one pictured has a old 70s style footprint gas peddle that I rigged to the throttle. So it idles very low... the lowest setting that would normally be on throttle control and revs up with the foot pedal.