I understand that PVC-E glue is the glue of choice for recovering the natural keys with new plastic. However, what is the best glue for installing new (real) ebony wood sharps? Any ideas?

Wood that has been ebonized is still wood. So is the key lever. This is a wood to wood application. Try the yellow carpenters glue or cold hide glue.

Are you referring to the fish based cold glue thats available through Lee Valley and a couple other retailers Dan? I recently started using this glue for key bushing cloth but am concerned about how it holds up to humid weather since its easily broken down with water. I use yellow wood glue for the wooden sharps with a little clamping.

Yes,
It is the ready mixed cold fish glue I was referring to Emmery.
Lee Valley is the place out this way.But for wood to wood I think I'd go with the carpenters glue.

Once the fish glue is dry I think you have to pretty much soak it with water to make it come apart. Or put the instrument out in the rain...that'll do it too.

For felts like bushings and damper plates I put one application on the felt side to make a smooth surface instead of a fuzzy one. Then the second application you get better bonding with the two surfaces...

There is no reason why the PVC-E glue would not work.

Wood to wood ..

Surface prep would be key.

Much the same as Maple to Maple .. Although the key wood is more porous.
Ebony or Maple sharps are certainly less porous and would require roughing up of the mating surface.