Justin
Cant say I agree with you on lumping your Jag but it was entertaining to
read about it. My 82 XJ6 had similar problems (coolant leak in the head
gasket) but I bit the bullet and put in a re-built motor. Cost A$4000
installed with 18 month warranty, etc. I did this because the rest of the
car is immaculate and I intend to keep her as a daily driver for as long as
possible. Of course, shipwrights disease set in and I have now all
reconditioned running gear, from radiator to diff.

Fazal
I do understand what you're saying and once thought like you.  Though now I think the benefits outweigh any concequences.  Weight transfer moves to almost 50/50, more power, better gas mileage (w/od trany) less cost in parts and maintenance.  My gas mileage went from 12/17 to15/20 and I can build a chevy 350 for the price of a valve job on a Jag 6.  You lose about 200lbs going with the V8 and with the gain in HP it's a win win.  You lose the prestige of owning a factory original Jaguar and it's true the resale suffers but the ride is the same, except in the corners of course, the car looks the same, feels great and you don't have to worry about a cat going out or an air pump dying and burning a nice brown spot in the middle of your pretty white hood.

Just for the record, I don't see us as purists or lumpers.  You own a Jaguar, I own a Jaguar, both beautiful pieces near perfect engineering and grace, and that makes us brothers in the same game.  I'd love to see pictures of your baby.

Humbly
Justin