No help here on a maker. While many Liege companies produced complete guns, the majority of Belgian guns were the product of a "cottage industry" system where a number of companies/families contributed to the production of a gun, so there was no single "maker" to put his name on the final product. We tend to think of that system as producing inexpensive guns, but in fact many very high quality guns were turned out that way.
It might be custom made, but also could have been turned out for a prestiguous dealer to show what he could have made for the discerning buyer.
In the absence of any maker, retailer, customer name, or indication of ownership, it is simply a high quality gun, and most likely untraceable to anyone.