Great progress! This is where I am with my manifold project.
http://usera.imagecave.com/phongshader/Locost_wk81/
http://usera.imagecave.com/phongshad...2/IMG_2905.jpg
http://usera.imagecave.com/phongshad...4/IMG_2921.jpg
I don't have the same manifold length constraints as you but the first prototype is still too long. I made the initial length to 4th harmonic resonant pulse @7500 rpm. I'll probably have to shorten the manifold by about 2" to have it fit inside the hood. It won't be as efficient but you have to make comprimises :-(