Thanks for your responses Norm, Max and MF.
Would still like to know if there's any other type of boss which fits onto a single slotted 23 mm B & S shaft.
Have managed to get this working satisfactorily, as you've advised it's just a matter of accurately lining up the driving edges of the two ears snug against the stamped plate grooves, and holding the wobbling bits in place while tightening the bolt with your third hand but not being able to eyeball the pieces as you go :-)
All of my other rescued mowers have a system of positively locating the blade or plate carrier to the crank boss with tabs, splines or several screws and the centre bolt just holds the boss firmly onto the crank. Same with all of the slashers I have worked on, and a gazillion other couplings.
A consumer item should not need an impact device when performing routine maintenance.
Otherwise it is a great mower.
