https://www.thingiverse.com/thing:5531131
They have worked so far using PLA plus material but I can't predict the durability. Manufacture using metal is possible of course. Different UNC bolt lengths are required and its all too easy to strip the threads in the manifold if poor quality ones are used.
The overall carb offset is slightly increased because I wanted to provide the maximum possible strength.
This is an image of the manifold side showing how the carb bolts are capitive.

I have used original standard gaskets but it would be possible to incorporate recesses for O rings if anyone cares to adapt the model.