Thanks for the links and leads, skeettx!
Apparently the Belleri are a gunmaking family in the Brescia/Val Trompia area who have for many years worked for the bigger firms in the area and also made custom "bespoke" guns for private customers and small runs of trade guns for various retailers,including in the US. The gun I found on Joe Salter's Gunbroker offerings is apparently one of the later. The truly custom Belleri guns all seem to be sidelocks or at least cleverly concealed side-plated guns (an Italian specialty, I think).
