Restoration worth the price?

[Ron Wood]

If I read the rules right, you cannot even replace the leather, if the old leather is all worn out and torn. The wood grips and the metal backing must also be original.

I don't believe that is a correct interpretation. There isn't anything that precludes restoration. As long as the stock/holster/grips conform to the authentic original configuration, they are legal. Look at the last paragraph of the second reference that John posted: " Therefore, any Luger or Browning Hi-Power pistol which would be removed from the purview of the NFA if equipped with an original shoulder stock, would also not be subject to the NFA is equipped with a reproduction shoulder stock which either duplicates or closely approximates the dimensions and configuration of the original stock."
However, there is no equivocation on the requirement that the Ideal sholderstock/holster may only be attached to an American Eagle Luger.