FF, I was thinking of using this stuff you used in your ambulance:
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F252376922308
Les Henson posted on here once that Big end knock is noticeable when pulling away or going up a hill in a high gear. At idle or sustained revs they don't tend to do it.
I’d start with looking at that steering - I don’t think it should be vague.
All the ones I’ve driven, that haven’t had knackered joints have had really positive steering.
One other option for your wife is to buy a series... My wife used to say my Td5 90 was really noisy and agricultural, 1000 miles in the series 1 later and she regularly comments on how smooth and quiet the 90 is.