Nice old wooden vise Pdparry. I picked up a similar but taller one last year that was bolted to an old wooden bench. I believe it probably came from your side of the pond as well. Possibly French. It is painted oak. The jaws are steel and attached similarly to your vise. Probably not the same maker but same basic design. A few pics for comparison. That's about all I know. Ed.
The two cross body bolts should have mounted it, the bottom strap with holes was used to keep it parallel, by placing a pin in one of the holes, then it stops against something on the workbench as it closes.
I should add that including the term Roubo in searches turns up similar vises. Some of them will be modern designs utilizing one leg of the bench for the back stationary jaw or other variations. There are also quite a few vintage examples or this style vise to be found, often still mounted on a bench.