While the leather was drying, I removed the old spine piece (saving the label), and cleaned the spine with methyl cellulose. I had to watch it carefully to the original end bands did not come off with the gunk. I pasted out the spine and lined it with Japanese tissue, which came up on to the end bands for additional support. Then I cut strips of linen, to fit between the cords, and glued them down with PVA. While the spine dried, I lifted the leather and end papers at the spine and corners of the boards. I reattached the boards by gluing the linen spine lining down under the lifted leather.
I pared and pasted out the new leather (one thick coat, let sit for 10 min folded over itself, add another coat) and molded it over the corners and spine. I also made sure to leave enough leather at the head and tail (after turn ins) to construct head and tail caps. I left this to dry over night.
The next day, I glued down the lifted materials with PVA. I glued out a strip of Mylar, and slid it under the lifted leather, tapped down on it gently, and slid the strip out. This ensures just enough glue gets underneath, and has less risk of the leather darkening. I also pasted out strips of Japanese tissue for the inner hinge.
While this dried, I worked on the spine label. I found a Morike similar in color to the label, and glued two pieces together. Then I glued the original label to the Morike and toned it to a better match with acrylics. I measured the spine width, and the height between cords, and cut the Morike to size. Then glued it in place with PVA. These are pictures of the end result.
I am going to try the technique on other books in the lab. The biggest problem I faced was building up my corners, which is something I need to work on. Other than that, my color is a little light, so the next time I will add a few additional coats of dye and dab them on with a sponge, to give the leather an aged look. Aside form dying the leather, this process didn't take much longer than a PC4 reback, and I like the end result better. Obviously the materials for this type of repair are more expensive, but I think it is worth it for the right books.