hey fred,
good to see another lad joining the forced m104 club.
i had a manifold built from a friend of myne,
the answer would be to go for a simple log style design based around the factory manifold like turbo e320 used,
probebly best bang for your $ option,
good luck, ask away on the open forum if you need any help along the way.
your gona have fun, an gona need some dedication