TUD.
I asked him the same question re the outer plate.
From a vague recollection of what he told me it's a plate with an additional outer bearing added by my pal. When he first fitted the Alton starter it was (as designed) operating on the overhung end of the c/shaft. Unfortunately after a couple of starts it caused the shaft to flex and 'spread/splay' the flywheels apart so when he rebuilt the engine he added his own outer support bearing.
The starter drive mechanism also incorporates four nylon 'break' pins which have broken on two occasions needing their replacement.