My interest in composites for my Marcos project started as a way to create a part that was too expensive to CNC machine out of aluminium. The V8 engine originally lived in a 2001 Range Rover - plenty of room under the bonnet. The Marcos is a much smaller car with a very low bonnet line. This has required a rethink on the inlet manifold design. While I can keep the cast runners, I have had to discard the single large throttle body. I will use two 48mm Jenvey throttle bodies. To mount these new throttle bodies I will need two asymmetric mini-manifold parts. Here is a rendered view of the CAD model...

Why not make a loose casting pattern and get it cast in aluminium rather than CNC'd.  Waaaaay cheaper and surprisingly not too challenging to do. 

The other option would be to carve / shape it from a piece of polystyrene foam and ask the foundry to cast from that.  Its a one-shot approach but works well.

Might also be worth a chat with Boost performance as they do a lot of RV8 stuff and might have something suitable.