Late 408, 409, 410 Part throttle kickdown
 

Having just fitted a newer gearbox in my 410, one of the bigger benefits is part throttle kickdown from 3 to 2. I recently came across what looks like a retro fit kit to add this feature to late 408 through to 410 - and possibly early 411.

727 3-2 Kick Down Module (1966-69) - A&A Transmissions

As far as I know it can be fitted with the gearbox in the car. I haven't used the kit and don't know for certain that it will work with our cars but I hope it's a good lead for anyone wanting to add this feature.