Model names:
Kyosho Optima Mid Custom Special
Kyosho Turbo Optima Mid Special
These are the last two models Kyosho made in the Mid series. Both with the stretched wheelbase.
I will update this first post with more info but for now, let's have some pics!

Gear diffs for the custom, balls for the turbo special.

Not exactly correct chassis but the closest I could find.

Fibre-lyte substitute for the turbo special.

A "look-through" view of the drive trains.