That is truly a remarkable piece of walnut! And a splendid rifle to boot. An observation though, if I may: highly figured wood, especially with grain issues through the wrist and lock area, have a tendency to be fragile. They don't take rough use like being dropped, or aggressive ham-fisted loading techniques. So advise your friend to treat it gently.
Congratulations on a really lovely rifle. And I would keep the cost of the wood under your hat. Knowing how it was stolen doesn't add anything to the rifle's value or worth, and only diminishes the character of the purchaser. Not that it's any of my business.