It's worth less "restored". Collectors want original condition. The more you mess with it, the less your gun will be worth.
Mechanical issues should be addressed, but the finish should be left alone.
Personally, I think it's worth $3000-$4000 if the bbls are good and rest of the gun is sound.
Greeners are great guns, but it's hard to get a long dollar for them.
OWD
BTW: I think it's some kind of early G-gun.
This Greener is made on a similar model action:
http://www.gunbroker.com/Auction/ViewItem.aspx?Item=257727463