more and more interesting I like the thinking on keeping the air and avoiding coils that makes a lot of sense
Definitely air. It simply redefines the ride quality. Otherwise at this age, given the snob cachet is pretty much gone there's little to set it apart from a good Disco.
I would suggest you get the youngest P38 you can and don't let others scare you away from the V8s, they are lovely engines with great power. Step out of one and into a diesel and you'll feel like somebody hitched an invisible skip to your tail. It'll either make you revvy or you'll want a power chip which will then mess with the transmission. Its true that V8s have suffered from slipped liners but in my experience if you keep on top of your cooling system (which is good advice on any car of any age) you should be fine.
I would then ask if the ABS accumulator has been changed and if in doubt I'd change it regardless. They had a designed life of 8ish years and many are still working fine (kind of flies in the face of the "P38s are unreliable" mantra) but do your pump a favour and get a new one.
Prepare yourself mentally to fully refurb the suspension at some point. You may only need to do parts of it which will then be a pleasant surprise rather than if your expectations are the other way around. Over time I have refurbed the compressor, changes seals and o-rings in valve block, replaced all 4 bags (2 at a time and generic Dunlop nothing fancy), replaced all the various suspension bushings and most recently changed the shock and steering dampers. I just went for sensibly priced parts, did most of the work myself and I reckon it cost me 600 quid over 5 years.
Transmission wise you'll want to check the diffs and the hi-lo transfer box, plenty of tips in the forum how. Then drain and refill all the oils (I have a manual btw, never had an auto of any kind so don't know how they work) that's gearbox, both diffs, transfer box. You may or may not change propshaft UJ and spicers and rubber matings (this is just cream, to keep the ride as quiet and smooth as possible). Generally though just grease everything that can be greased.
And that's most of it! You'll have niggling electric faults with windows or alarms or the radio etc but nothing to keep you from finding your way home to tackle later at your leisure. My car gets very rough use, I try to take care of her and she in return has never failed to deliver me safe and sound even if she had to limp on 3 legs to get me there, and
that's what sets the RR apart from anything German, Yank or Oriental.
(ps. P38s are far, far easier to work on than L322s and parts are much cheaper so keep that in mind.)