According to Boswell in Boswell on the Grand Tour I, 1763-1764, "an Italian nobleman of ancient family, not rich, but very knowing and extremely clever."
According to the editors of The Journal of his German and Swiss Travels, 1764, in 1764 Cavalcabo "had been trying for several years to find employment and, more importantly, to regain the lands and title due him as descendant of the marquises of Montferrat [...] He would be last heard of [in 1766?] when named director of the Office of the Prussian Lottery in Hamburg."1
Life with Boswell:
The Marquis, on August 13, 1764 in Brunswick, told Boswell about the supposed ability of ice to cure "a weakness of the stomach and a relaxation of the nerves", and promised to teach him his ice-making method. They met on a couple of other occasions before Boswell left Brunswick for the last time on August 22, 1764. After their last meeting on August 21, Boswell "found him the true bon catholique, for he talked with ease of having women, and yet told me of a distemper that he had brought on himself by fasting".
Note 1: A footnote on p. 74 of The Journal of his German and Swiss Travels, 1764 gives some further interesting details about the Marquis' unsuccesfull ventures in life.