I bought the wheel kit for mine a few years ago and it made the mantis so much more of machine because it gave you total control of the machine. My unit is 90’s machine and the wheel set bolted right up. If primer bulb has hole in it, you need a new one.
Sorry I don't understand the question "what is the diameter shaft?" The wheel set has a flat flange (1" x 1/4") that can adjust to different heights on the horizontal, y-shaped bracket that attaches to the Mantis. These all are part of the assembly. The bracket also measures 1" on the flat side.
The Wheel Set is only compatible with Mantis 7000 series tillers.