No shift lever on transmisison cover. But rather a lever mounted below the steering wheel. Can shift on the fly. Known as a planetary gear drive. Starting, stopping, and selecting gear ratio is done without a standard clutch. 3 types of transmissions - all basically similar but PTO's are different. 1. without a PTO 2. w/ a 540 RPM engine driven PTO, 3. 540-1,000 RPM engine drive and a ground speed ratio PTO.
3 elements of a planetary gear is the sun gear, pinion carrier, and ring gear. When any element is rotated, the other two elements will also turns unless one is held be an external force. And it gets better. The Vintage Tractor Resource link can explain the SOS in detail with a diagram too.
Aren't you glad you asked?