It would take many many hours (and much expense) on the part of a really good gunsmith and engraver; and it's most likely a replacement frame would never properly fit the original stock, but the gun could be restored were someone that dedicated. If someone were to attempt a restoration, they'd need to begin with a salvaged frame Grade 2 gun or higher as those graded frames already have the frame properly shaped for a high grade gun; all lower grades would require the breech balls be filed and contoured to high grade gun profile. As to the second style joint check, this was designed and used on some early auto ejector guns (never seen it on an extractor gun); but was discontinued when Hunter determined it unnecessary. The biggest issue with that device is that if it ever breaks so that the pins won't retract from the frame cuts, it is almost impossible to remove the barrels from the frame.