Thought I'd advise this for the benefit of those running Jag XJ6 front calipers.
Here is a supplier in the UK. of Alloy calipers as a bolt on option for those running the heavy cast iron Jaguar Calipers.
Kit 6: Billet aluminium vented front kit | cooper
Also Spiteri in Melbourne claim to be in the process of manufacturing a similar Caliper. However, There is rumour the Spiteri caliper will require larger diameter rotors.
Andrew Spiteri is the boss man if any want to have a chat with him regarding their version.