Andy, Great thread and which reminded me to post this option for lightweight alternatives for Jag XJ6 front calipers:
Kit 6: Billet aluminium vented front kit | cooper
Bolt on alloy replacements for the heavy cast iron XJ6 units. Comes in choice of anodised colour, with stainless pistons, seals and competition pads.
Simple bolt in replacement.
Edit: fits 15" rims