I was looking some time back on one of our member-contributor’s websites (I forgot which one now 
) and I noticed on there that when he went to replace his valve cover gaskets (and half-moon seals) he first pulled the intake manifolds. Please tell me that isn’t a requirement just to be able to pull the valve covers, at least on our face-lifts (his tutorial didn’t cover that topic). 
(btw, he had a '70s model - pre H.E., if that makes a difference).
On the V12, absolutely a requirement. On the 4.0, I dunno, probably not.
It’s not difficult to remove the manifolds. 24 nuts and a couple of hoses disconnected and both manifolds and the injectors all come off as one piece.
The fuel injectors, meaning the entire fuel rail ??? Well, I guess it could be worse - it could be the exhaust manifolds that have to come off … ! 
Valve covers come off with 13 bolts. Nothing needs to be removed…except the wires to your spark plugs!
I will be doing this for the first time on Friday. Will let you know how it goes. Looks straightforward. I’ve just read sometimes a few rubber hammer blows may be needed to get the manifold free. I also am very afraid of dropping something into the intake valve openings, as they are DOWN instead of across like other engines I’ve pulled intake manifolds on.
I still don’t understand why they must be removed … is it a matter of “space”, i.e. to have sufficient elbow room to remove the covers? or do the manifolds actually block access, e.g. to some of the cover bolts? 
Dallas, the intake manifolds come over the top of the valve covers.
Your profile shows you have a 4.0 liter. Are you asking about the 6 or V12? It’s real obvious on a V12 that the intakes have to come off if you simply look.
I meant the V-12, but no, I haven’t looked at the engine before with an eye toward removing the valve covers, just noticed on the contributor-member’s website that he did that and wondered why … 
(and actually, as has been pointed out before, I own both a 4.0 and a 5.3, and they are both listed on my profile - also, I have r/red the cover on the 4.0 before).
Thanks everyone … 
If you could get to all the bolts holding the valve covers on, you still wouldn’t be able to pick the cover up high enough to clear the cam when removing it.
Wow. What a friggin design … but then hey, it’s a Jag-uar … 
Not that uncommon on V12’s with overhead cams. Mercedes 93-99 S600 V12’s intake manifold is even harder to remove to get to the valve covers. Jag intakes are easy by comparison.