Irish > I've been cheating! I temp wired it straight to the battery with no other electrics connected. I didn't want to fire it up until I knew it was shimmed properly.
Chris> I'm going on the side of too much rather than not enough!!
Ok, up date for tonight:
Found the paperclip! Borrowed a better battery with increased CCA. I finally got to 4x shims on the outer pad and it's nearly there.
The better battery throws the bendix right into the ring gear and meshes nicely. I think the previous battery only threw the cog in a few mm instead of fully across.
The only problem I've encountered now is the outer bolt has pulled the thread

so I'll hunt for a longer bolt to reach the fresh thread or gently re-tap it to accept a bigger bolt.
On a positive note, I discovered a tapped hole in the corner that means I should be able to fit a hi-torque starter at a later date should I need to!