Blank slates can be any side plated gun. Bakers, Lefever, Smiths or even a small bore Crescent. I would pass on the Smith they have a well earned reputation for cracking the stock. Any Sterlingworth is a candidate as should be many of the early A grades with no condition left as collectible guns.

Find a gun with good barrels and one that is on face and you are in good shape. Never buy a project gun, for an upgrade which will cost hundreds just to get the barrels and action into safe shape to shoot. Better to put your time and money into other areas of the project. Like wood and fine scratching.