The easiest (and cheapest) way to make your set of U.S. Grimsley harness more appropriate for Confederate impressions is to swap out the Valise Saddle for a simple Confederate version.  While the Valise Saddle as specified in the Ordnance Manual served a functional purpose, both in carrying a valise and connecting various components of the harness together, it required an excess of materials and labor to produce.  As early as 1862, Confederate arsenals were replacing Valise Saddles with a modified version of a carriage saddle, and by 1864 this replacement became standardized.  Just a simple pad with a girth, billets for the Belly Band, and a Back Strap to connect the hames and collar to the crupper and loin strap assembly, this carriage saddle will buckle right into your harness where the Valise Saddle had been.