This is a good discussion to have.
AFAIAC,all the main parts must be original to that serial number. Stock, action, barrels, triggers, forend, trigger guard. Replacing or repairing the small parts within to restore function is OK to me. If you start replacing pieces to make a more modern firearm, you are modifying, not restoring.
Refurbishing barrels, steaming out stock dents, these things are an attempt to return to a "prior state". So I consider them OK.
But I come from the antique furniture side in all this. Original technique and materials count there.
I completely agree ..........when you start grinding out metal such as changing the chambers, cones, chokes, stock dimensions to so called modern, recoil pads and the like, you are modifying.........period.........not restoring ......
Example on this old gun of the same finish materials and methods as in 1912:
I personally don't like years of other peoples "closet dancing" marked all over my guns.....
The biggest cop-out is the statement....'I like my gun as a shooter', meaning it is a less than stellar gun, kind of banged up....?....a gun can be pristine and shot every day......by someone who uses care and also uses the gun as a gun, not like a shovel or machete.......
You've heard the comments like....'has three dents in the barrels, but
does not effect operation.... 
