24V CAV starter refurbishment questions

[caperover]

Finally yanked the starter after nothing but cicada-like sounds when the starter button was pushed.
Needing an adventure (at the age of 74) I removed fender, heat shield, and dropped exhaust pipe in order to reach through a goopy mass of oil and tar to bolts and cables. So much fun, so little time. I have decided this is a bourbon project, not a beer one.

Lo - the studs backed out of the flywheel housing easily, and I can ease (drop) the starter between the frame and the floor into a carboard box.
Upon inspection, there was only one 7" bolt holding the starter ends together...yikes. Things area bit loose. I lift and tied up the brushes with cable ties, removed the one remain 7" bolt, and eased the rotor out of the casing. Commutator is a bit pitted, but not work. No electrical smell. No solder thrown everywhere. Front bushing seems a bit wobbly. I'll check continuity on the windings, but things looks intact.

After carefully removing a bit (well, a lot) of tar from starter, it reveals it's a CAV unit.

So:
A. - What's the story on CAV starters? Were they in cahoots with Lucas or just an alternative supplier to Rover? Were they just a supplier of FFR parts?
Are there any parts interchangeable?

B. Anyone got a 7" threaded rod/bolt to replace the missing one? Used is fine.

C - Are there any shops in the New England area (or maybe beyond) who will rebuild this grease and tar sodden specimen or do I need to get a new/refurb unit from gwd knows where. I'm looking for suggestions and experiences here.

D - Am I now at the point where it's more cost effective to convert to a 12V system?

Many thanks for constructive advice.