Thanks for your suggestions Gentlemen. In regards to several of the comments below:

"Also best to find out why that happened before it's repaired" - As to the gun itself, I don't know the history of this gun except that it was owned by a California collector for the last 25-30 years; so have no idea as to what may have happened to cause the cracking; would be very interesting to find out. Also need to know if there is damage inside the frame that isn't visible from the outside..

"Is there more than one high grade shotgun with those specific cracks in circulation? I seem to recall seeing them previously." - Clearly this example hasn't been in circulation for at least 3 decades and I've no idea as to other maker's guns (except for Flues model Ithaca guns); but I've seen lots of Smith guns, and more than my share of high grades. This is the first Smith gun of any grade I've ever seen with this kind of frame damage. That observation noted, I've been told that Marlin had a number of Smith frames to crack early in the Marlin production era while they were experimenting with changing the hardening process from the old bone charcoal method to the less expensive cyanide process.

"My first question would be why did the cracks develop" - Mine too; and as the current set of Damascus barrels are not original to the gun (although they are graded A-1), my theory is that the original barrels were destroyed by an overloaded shell; the recoil being so intense that the barrels were slammed backwards with such force that the barrel lug damaged the frame at the back of lug cut. If so, that may also be the reason the original stock was destroyed?

At any rate this was one heck of a double gun when new, so if there was ever a wrecked gun worthy of restoration perhaps this is an excellent example; but also obviously expensive. The owner is aware of that fact but is determined to do it "right". Tom