Hey Ed,

In looking at the pictures in the first post, it appears you have the belly pan with the indention for a tuned pipe to run right down the center of the belly. With the pipe running under the belly, you shouldn't have to change the tail's anhedral. When I bought my Illusion, the builder had already cut the front of the fuselage for the engine to be mounted with the glow plug at a 225 degree angle (looking from the front) so the header will exit right under the center of the plane.

Just my $.02.................

David