I`m also in Herts.
I would try, in no particular order :
Harris Mayes in Rickmansworth - 01923 711800 - look after my TD5 110 and used to look after my LSE as well till I sold it, very knowledgeable and enthusiastic and will lend you a courtesy car. Peter Harris Mayes is the guy to speak to
Kings Langley Land Rover - re-chassis`d my ex military 109, always used to be a bit pricier than Harris Mayes on workshop rates but very good as well. Might get it done cheaper if you let them do it at Thame Land Rover, which they also own and isn`t as busy. Both ultimately owned by the same guy who owns Chipperfield Land Rover - the main dealer for SW Herts.
Oak Tree Garage in Wheathampstead - looks like a bit of a shambles but is a real Aladdins cave for bits and also did service /repairs when I used to go there, nothing fancy but don`t cut corners either.
My vote would be Harris Mayes but ring them all and see what they say.
And no I`m not on commission
I should also say that if geography isn`t an issue and at the risk of embarrassing him I`d see if James Martin was interested in doing it (via a PM in the first instance) - I`ve been impressed by almost everything he has to say on here so far