I have created a performance Fiat 850 intake manifold for various Weber carburetors for use in a Fiat 850-based car. I took design inspiration from the Alquati and Cabeza de Vaca - hopefully taken the best from both. First, I have tiled the manifold by 6 degrees. The outlet has been slightly enlarged roughly 2mm in all directions where it meets the cylinder head (based on the Alquati manifold). The plenum necks down to 31mm to match John Edward's Cabeza de Vaca intake design.

The mounting flanges are roughly 11mm, the plenum wall is 5mm and it is 79mm tall. The carb mounting holes are 46mm x 93mm and the venturi holes are 36mm - good for the Weber 32/36DVG or the 36DCD, etc. You will need to tap the four holes on top to insert studs or drill them out for bolts.

Print with support enabled. Print this out in plastic and, if you like the result, have it printed in aluminum and install it on your car!