Indeed I've considered the 'rusting immediately after cleaning' issue. I was hoping to borrow your trailer Tim to take it up there, but seriously thinking of hiring a covered trailer to collect it. One of my questions to them is if I can arrange to collect it direct from treatment without it going outside (given the time of year). That said, they cover this issue on their website and say that if it's returned for electro coating it will be given a brief acid "clean up" then rinse to rid it of any surface rust before treatment.
As for the earthing, this car was built positive earth but converted by the previous owner in the last 10 years... still running a dynamo though rather than an alternator conversion.
And speaking of conversions, I made the required donation to the Jaguar Daimler Heritage Trust to get certified confirmation of its original build specification. Turns out it's definitely what it claims to be (3.8 ltr, rhd, gunmetal paint with red interior) except that it was originally an automatic rather than manual. Guess that explains why the the hole for the gear stick looks like it's been hacksawed out of the tunnel!
Don't suppose anyone's got a Borg Warner DG 250 gearbox lying around unwanted?