There is a reputable fellow in Texas who has been putting GM 350 engines and turbo hydramatice transmissions into Jaguars for many years and his business is thriving; his bread and butter business comes especially from the XJ6 and XJ 12 sedans

He writes an amusing, long newsletter you can read in Hemmings Motor News, and that might be a good place to look for more information

I think his business is called John's Cars or something like that (sorry I don't have the website)

__________________
1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)