Ransomes tool

Removing the  landroll drive sprocket from a Minor, Mercury, Marquis or old Matador  can be a bit of a faff particularly if doing it single handed . I've made a tool to grip the sprocket  and  I want to make another tool to hold the other slotted  end of the shaft but will be interested to know  whether Ransomes sold a special tool for the job or anyone has made one. 

At present I use a 1/2 drive Stahlwille brand flat bit that I believe was sold as a "track adjusting tool" that I bought on spec years ago - on the end of a 30" foot breaker bar! Does the job but is difficult to hold in place while trying to undo  the sprocket (lh thread).. What I have in mind is a plate that will bolt to the side of the machine using three roller bearing carrier bolts to hold the flat bit in place. 

Will be interested to know how others tackle the job !