Don't know about an IHMSA two gun set of Ruger "Silhouette Super" SBH's; sounds incongruous.
The boxed "Silhouette Super" configuration came with the original tapered 10-1/2" barrel with silver soldered ramp front sight, and the standard length, anodized aluminum ejector housing. I was involved in design and placement of the IHMSA rollmark. The rollmark was ordered by Elgin Gates and sent to Ruger, where it was applied before bluing.
I cannot tell from which wood the box is constructed. It may have been called "walnut," or perhaps the wood was unnamed. Resembles mahogany more than walnut. Since mahogany forests have generally been stripped, I suspect the wood may be black birch, a mahogany look-alike. Black birch is also called "sweet birch" and "mahogany birch." (Black birch is straighter-grained than white or silver birch, which don't resemble mahogany at all.
The box came with a rectangular cast brass IHMSA logo, filled with yellow enamel. If you have a photo of a two-gun set, I'd like to see it.
Ron Ricci and others may be able to provide more accurate info on this, or these, IHMSA editions.
David Bradshaw