I just went through and upgraded my Jag front for the 2nd time. I made new hubs to suit a hat style rotor as there are more performance rotors readily availble in this style. The ventilation on the hat style is also better in my opinion.
I made my own hubs but Willwood or one of the other brake kit manufacturers will probably be able to supply hubs to suit the Jag spindles.
I also went with radial mount calipers because I reckon they are easier to make mounts for than lug mounting. There's probably a few pics in my gallery of making caliper mounts.
Here's the tread I did on the front brake setup:
Jag front brake conversion
Cheers