Glad you got the oil pressure thing worked out.

Your ticking must not have been the 'loose liner syndrome' - which is really loud (sounds like a big 1.5 cylinder diesel engine is deep inside the engine).

I suspect you just had a low oil pressure at idle speed, which coupled with the typical main-bearing clearances you'd be seeing with 140K miles meant your tappets weren't being pumped up sufficiently. It probably wasn't all 16 - instead you'd have one, or a few that drain down and needed pressure to keep them pumped up.

I doubt it was your other two suggestions about the pump slap or the timing chain.

 

Thanks Dave for the input! Learning more with every Disco mechanical misfortune. This car is a far cry from my original 1969 VW van or Nissan 4cyl 4x4. Now if I could get through my 340 code, I could move onto some fun stuff- like new suspension...