This is it's starting stage. It was missing a few chunks, and covered in scotch-tape.
First, I carefully removed all the scotch-tape from the front and back. For parts on the front, to avoid peeling up text, I used ethanol to ease the adhesive off slowly.
The piece disassembled. At this stage, I cleaned and de-acidified all the parts.
The finished piece: I salvaged as much as I could, and mounted it on matching kozo paper. The large pieces were patched in the front and back to match the density of the original paper. I decided not to continue the border, and did as little touch-up as possible on the actual design.