John,
Sorry the customer rejected (honest, I didn't call them!!!)
As long as they want velvet, the wood is no longer an issue. Poplar or pine that is painted (yes, they still make paint penturners!!!) black will make a nice display and, oh yea, cheap!!!
I have seen other pen displays that take the purchased "leatherette" displays with the grey interior and "class them up" by laying a piece of acrylic over the pens. The acrylic is custom cut to just fit the opening. Sounds hokey, but it really looked good and kept fingers off the pens.
Might try to adapt this idea. If you can make it "laying down" with about a 20 degree incline, that would be nice. If you are limited to a 6 inch deep shelf that this will fit on, it has to be vertical (or nearly so). Your dimensions become more critical to keep it from tipping over. Customers are not smart when they reach to "grab" things and, if it falls, it will unfailingly hit the most expensive thing in the display case and break that item!!! (Have I mentioned, my other half displays glass!!)
John, you clearly have a "good eye" for displays, so I leave the details in your competent hands. And, if the end product looks good to me, I will call the customer and tell them to accept this one. [:0][:0][:0][:0][:0] (See signature line)