I almost can't believe it: I have been able to successfully blend with my drum carder! Ever since I bought it, I've had no end of troubles, and last year I put it into the top of the closet to forget about it.
Well, with my scheme to blend the sheep shares fiber with the polwarth, I realized I couldn't blend it all by hand and finish it with any enthusiasm left to actually spin it. So, I broke out the ol' drum carder. It's a Louet Roving Carder, which was all I could afford when I decided to buy a drum carder. Cruising around youtube, I discovered a video of someone with my exact carder. Using the video, I've been able to blend up the two fibers - no thick spots, and the only neps are the ones that were in the fiber to begin with! I'm so happy.
I've adjusted the scheme a bit. I'm going to try some number magic on the shawl: a singles of the polwarth, a two-ply of the blend, and a three-ply of the cormo/mohair. I've carded up the blend and spun one bobbin of it. It spins so smoothly... I think I'm going to go with a navajo ply for the three-ply, mostly because I don't know if I can find all my bobbins. We'll see.