Hey, thanks. They look better in the pictures than in person, but I'm looking forward to hearing them. If I hadn't been so impatient, I'd be ordering the kits now, but it's been interesting so far.
You're right, the angle of the sides would vary on the tractrix. On a straight sided conical the angle should be the same all the way. I was able to cut the verticals along each edge and when I propped up the bottom piece to a reasonable angle I could just set the sides in place and put the top on, and it would sit there like a house of cards. I looked all around and all the edges were flush. Neat. I glued and screwed it together and the next day the tops and bottoms had warped inward about 1/4" at the center. I had to build a little brace with a threaded rod to push them out when I glued the horn to the cabinet pieces. Those kits are sounding better all the time, but I'm learning.