Rory,

First, thank you for the excellent advice. And if I may take the liberty I admire you volumes on the Duke very much. I think they update Longford excellently. (I would ever wish to have her replaced).

You might be interested to hear more of my digging, which sadly was begun back when I was much less academic in my note-keeping.
I got the name of the owner of the house by complete accident. A letter from a Mrs. Disbrowe revealed it, and some other interesting particulars in this book, ‘Old days in diplomacy; recollections of a closed century’ a record of the life of Edward Cromwell Disbrowe, by his daughter.

https://archive.org/stream/olddaysindiploma00disbiala#page/114

From there I was originally directed, if I remember correctly, by an acquaintance on twitter who knew Petersburg, towards Kutuzov Embankment, as being the present name of “Great Quay” because it was near the British embassy I think (In old maps the river is called the Great Neva). However nothing could be turned up except that “Gourieff”, was actually a Count not a Mister, and was indeed Tsar Alexander’s Minister of Finance and had some correspondence with President Quincy Adams. (He’s also famous for a fruity semolina porridge).

Finding the specific house has therefore been quite difficult. Thus far maps etc don’t mention it, and travellers etc who do mention the Count don’t usually specify where he lived. It is also possible he had a number of houses in the city. Yesterday I got a hopeful lead from a gentleman in Russia on Facebook (now and then Social Media is very helpeful). He very kindly told me that Count Guryev’s house is (traditionally) Number 27 on the Fontanka Canal. (Only the lower floors of which date to the 1820’s)

http://www.citywalls.ru/house26.html

“В 1810-х гг. дом перешел в собственность министра финансов графа Д. А. Гурьева, известного нам рецептом своей знаменитой манной каши с фруктами, миндалем и специями.
В 1825 г. принадлежавший Гурьеву дом арендовал австрийский посол Лебцельтерн, женатый на Зинаиде Лаваль - родной сестре жены С. П. Трубецкого, одного из лидеров декабристского Северного общества. Сразу же после поражения восстания на Сенатской площади здесь находился С. П. Трубецкой и в ночь на 15 декабря был арестован.“

The crux being (thanks to google translate) that the Count indeed lived here, though it was later rented to the Austrian Ambassador.

Unfortunately, Mrs, Disbrowe’s letter (based I surmise on second hand information) says nothing of the Fontanka, and though due to her getting the Count’s title wrong I can hope she also got the location of it wrong, I must continue to dig in order to resolve the anomaly. Your suggestions will help me greatly in this and in addition I’d very much like to read more of this trip anyway.

Thanks again,
Josh.