Jeff, regarding spare rib dimensions, I presently have six, 2-slab cryovac'd packages in my freezer. I grabbed the biggest package and got the following dimensions:
length: 18-1/2"
height: 8-1/2"
thickness: 3-1/2" (for 2 slabs, so 1-3/4" per slab)
Granted, these are frozen packages...