when I mentioned phenolics, I meant pre made blocks of fiber reinforced phenolic resin. it is about as easy to machine as wood, and like you said responds well to adhesives.
I had another thought today, what about masonite, the brown fiber board stuff they make peg boards out of, just buy the stuff without holes. I think it usuallly comes in 1/4 inch thick sheets, 3 pieces could easily be bonded together to get 3/4 inch, and then machined to the desired demensions.
It could even be made bigger than needed, and then bored out to a size large enough to accomodate a plastic tube or similar with a ID equal to the TB bore, which would be inserted and bonded into the masonite spacer block, to, 1. make a smooth surface, 2. make a good seal as masonite is also porous, and 3. to prevent fibers from being injested into the engine.
