So is there a way to upgrade the 07 - 09 XKR, 4.2L Supercharged engine to get to the 510 BHP rating for the 2010 XKR? Or am I missing anythign like mechanical changes/upgrades at the Jag factory?

Edit: Sorry - I missed/forgot about the upgrade to the 5 liter engine.

So aside from the supercharger pulley for higher end power, what low end bolt-ons or changes are there?

 

Here's a good start: XKR 2007 Modified by Paramount Performance MASSIVE POWER!!!! - YouTube