Raimey - that is an interesting gun, minimal engraving but a fancy trigger guard inlay, rounded front lump and disc-set strikers. It also looks to be one of a pair(?). I don't have the information on hand unfortunately but I can post some information on the Helicobloc patent in a few days from one of their catalogs.

The top-lever stop is present on m V-C as well.

Such a long, long time to be gone, and a short time to be there.