I owned and partially restored a rare 1973 Series 1 V12 for a few years. It was reasonably reliable for its age and still surprised many passengers with it's "magic carpet ride". Whilst it may not have been as fast as a V8 conversion there really is nothing like driving a V12 (despite the fuel consumption from the 4 Stromberg carbies!), when you put your foot down there is no kick in the back just a very refined 'whoosh' as the rear drops slightly and it takes off. I loved the straight lines of the V12 grill as opposed to the "egg crate" grill of the XJ6 and in the series 1 the wings on the boot lid were far more preferable to the larger boot handle introduced with the Series 2.