Because these cases are for Reid, I thought I'd make sawtooth shelf supports for them. These supports were a common method of providing shelf adjustability in the days before shelf pins and standards. A strip with bird's mouth cutouts is attached to each inside corner of the case. Cleats are made to fit the span between the cutouts, as you see in the photo below.
Making sawtooth shelf supports takes a lot more time than using pins or standards, but they add a nice handmade touch, I think.