I wouldn’t go with Mansfield 4x4 in Bury St Edmunds (IP32?). They’ve screwed over quite a few of my mates who I’ve sent there for Landy work. They used to be a reliable LR garage but now they are greedy bastids.
I replaced the corroded webbed earth strap with a 10AWG cable from the firewall to a bolt on the LH side rear of the V8.
No issues going on 3 years now.
There are electric fob types of battery cut off switches assemblies on eBay which are cheap. They are easier to install and can disconnect all electrical system power from the battery.