Thanks for the responses. I'm happy to stick with self propelled as this mower will be used domestically on large lawn areas where self propelled is enjoyable.
The motor and base are in such nice condition so I'm willing to tinker. I guess I'm curious because the design around the rear axle is so close to a 216 and if can be a easy straight swap out of the older 2 speed, I'd source the 3 speed for that extra speed in 3rd gear.
