What are you willing to spend? I think the going rate on a leather covered recoil pad is something like $3-400, having Mark do grain painting will add to that cost, I imagine not insignificantly.
The comment above makes a lot of sense. Considering that the current stock wood does not appear to be highly figured, the total cost of a leather pad job and fake grain painting has to be closing in on the cost of a factory equivalent restock. I emphasize factory equivalent because I understand that the cost could be significantly higher if you demand perfect execution by a high dollar custom stock maker, and exhibition grade French walnut.
At the other extreme, the cheapest way out would be a decent lace on leather pad that covered the non-matching wood extension. The nicer ones aren't terribly hard to look at, and are a viable solution for a gun that isn't valuable enough or used enough to justify spending a lot. And I'm surprised that no one has mentioned a butt transplant as yet another alternative.
