Paul
By the time you see this it's probably too late but I would stay well clear of an 89 XJ40 (Daimler or otherwise) - looks horrible (IMHO), dodgy electrics etc. you might as well buy a nice Series 3 4.2 - beautiful and easy to mend.
For me, the best choice will always be a 4.0 AJ16 X300 in whatever guise you can afford - pref. XJR

This is acknowledged as the best straight six engine that Jaguar ever made - and thats saying something!
Tho' BB will tell you that a V8 is a cracking bargain if you get the right motor ie no Nikasil probs. timing chains and tensioners all sorted, pref. history and all the expensive electrics/computer generated bits work properly
Regards
Dh Dove