I'm going to do a diff swap and the new diff came with a set of brakes already fitted so planning on swapping them with the diff.

Disks and pads look OK on the replacement diff, but maybe worth getting the pistons out to renew the seals?

Best place to get the seals?

 

David Manners, ring them up and ask for Jack Weston, Big Red in Worcester, or look on ebay for a set of genuine Girlings. Often aftermarket kits are not as finely made as the originals.
Setting up and improving the handbrake is as, or more important. Impossible to do it on properly on-car. See this thread:
https://www.jaguarforums.com/forum/x...onvert-243218/

https://www.biggred.co.uk/