And hello to you too!
Although I occasionally find the Where Was I conundrums tricky, I can usually get started within just a few seconds, simply by looking for the 'Friend' hint that's nearly always near the start or end of the text. Today it appears to be "an impish grin crossed Friend's face: like the one in a famous carving in a church". The only famous imp I know of is the Lincoln Imp:
https://www.visitlincoln.com/lincoln-cathedral/the-lincoln-imp
That led me to search 'constable of Lincoln castle' and the first link offered by Google seemed to fit what's needed.
Also, looking at the Wikipedia entry for Lincoln Cathedral shows that it was claimed to be the tallest building in the world in the 14th century.
I've not taken it any further, so I might be barking up the wrong tree entirely, but that looks like a promising start to me ;-)