I too can recall that the Frankland Brothers offered a service for re-surfacing cursors.
How they went about doing so, I am unsure, but I am reasonably familiar with metal spraying such as molybdenum, although it's an age since I had any done.
To my mind, there must be some of us think that the recent developments in Lambretta tuning somewhat baffling.
After all, those of us that struggle to find 'standard' components to operate just four gears effectively, must surely be being a bit 'picky' as you never get to hear about any downsides with selection using the current choice of five speed 'boxes.....
Does that mean the manufacture of the five speed cursors is all 'sweetness & light' or are very, very few riding full bore changes with these set ups?
To my mind, the principle of alternative gear manufacturing methods has allowed for five gears strong & wide enough to occupy the space of four could now be best applied to..........(wait for it).........just four gears made using the same principle with correspondingly wider cursor dogs........
As for clutches, a good solution is to do what the sellers of uprated clutches do. Adapt a motorcycle clutch to fit. I managed to do so & it was excellent.