Hi Akitaman,
I am blown away by the work you do.
Anyway...the Alfa 6 sedan had 6 one barrel cabs so you can try to find a manifold from one of those. The only other V6 with carbs was the South African special 3 liter GTV6s. These are ultra rare, even in South Africa. The heads are also a little different on the carb V6s so that's another factor.
I think it would be a lot easier to use fuel injection, Gotech, Autronic, SDS etc. Of course the sound of 6 carb barrels would be cool. That alone might be a good reason to use carbs.
Greg,
www.hiperformancestore.com