Hi Justin,
My thoughts on your earthed keel...
I would deem it unnecessary although American yacht forums have shrouds, masts and keels all connected because they seem to suffer a large percentage of lighting strikes when they're out on the water but even they disagree about whether the lightning conductors should run inside the cabin or just a wire dropped over the side when sailing because of safety concerns to people and the damage the lightning strike can cause to the boat hull
Although it can happen what are the chances of a lighting strike on a boat in the UK?
Should every home in UK have a lightning rod on the roof?
Seacocks made from bronze react very little with seawater it's where two dissimilar metals connected in sea water that corrosion occurs so if you link all these different metals like aluminium, iron, steel around your boat then there's a good chance there will be a potential difference between them and sacrificial corrosion can occur.
Your engine block is 'connected' to the sea through your prop and cooling system so the zinc anode corrodes to protect the 'iron lump'
The choice is entirely up to you.
Your LB system seems fine, just remember to ensure fuse panel is not linked to engine battery when starting engine.
Stevie