Jim: It is quite possible that grand dad removed the bushings and pins in response to the propaganda against damascus barrels in the 30s. Before shooting the gun, you should of course have the gun checked by a double gun specialist smith. Let us know where you are and we might be able to recommend someone nearby http://www.lcsmith.org/faq/safetoshoot.html
The vast majority of 00 and 0 grade 12g Smiths were ordered in large lots to be sold by sporting goods and hardware dealers, but you might consider a Research Letter which could identify the original purchaser http://www.lcsmith.org/shotguns/researchdivision.html