Stuart,
The battery contact switch does not have much adjustment, but I will ask my starter/generator rebuld guy if he has one with more, or slots instead of holes.
The joints are all sloppy, but a spring in the system takes most of it out. The starter drive gear must be quite a bit harder than the ring gear on the flywheel as it does not have a mark on it.
Would the switch to 12 volts make the starter spin faster?
Stewart