Besides the obvious displacement difference, what are the differences, cosmetic and mechanical between the 5.3 and late model 6.0 V12s? Are there any sites that discuss the differences?

 

6.0 is cleaner looking under the bonnet, has more pick up/power and a more modern trans hooked to it, that being said you still have to deal with those tail lights!!!!! whoops, there I went and started something!

http://www.jag-lovers.org/modern/mguides/jl0206.html

 

Crank 78.5mm stoke compared to 70mm early 6.0L used forged crank and later ones had cast crank
Sleeves are slightly shorter to clear the rods for the longer stroke.
Pistons have a different pin height. SAME bore
Heads have a larger chamber than the 5.3
Fuel rail and injectors are O ring sealed
Inlet manifolds have different mounting points for fuel rail
Bellhouse has a different bolt pattern for the 4speed GM box
Water pump inlet does not have the thermal switch for aux fan.
AC compressor mounting is different for the smaller compressor.

I have probably missed a few things but this will be close. There are also differences between the saloon and XJS 6.0L like the water Xover pipe.

 

I noticed that the air intake on the later v12s went to the top of the radiator and got fresh cool air. Can my '92 be upgraded so ?

 

Yes, this is what TWR engineered for the XJR-S with larger inlet trumpets for air boxes and high flow filters this was apparently worth nearly 20hp alone. If you don't mind cutting a couple of holes the air can be ducted from behind the headlight, there is enough room to duct it from the side of the radiator at the top.

 

ooooooooo holes.!!!!! the good thing about the newer models was it didn't need holes.