My personal thoughts on this, I am sure you will get more ideas.
If possible you need to make a lining that will accommodate some of the pages, front and back, that may not be real important to the contents.
The lining would be stitched to the cover, the book held in place by the pages slipped into the lining.
If you are not going to carve the cover, use a light weight (3/4 oz.) fine grade of leather, you can buy book binding leather. I would then consider gluing
the cover to the spine of the book but only if there is none of the original spine left.
Before starting something like this, read as much as you can on book binding and covering/recovering old books. There is a wealth of information
about this subject on the Net.
One last note: I wouldn't use anything heavier than 6/7 oz for the cover if you are planning to carve.
ferg
ferg