I have an A14 in a Triumph Spitfire. There's about 4mm of clearance between the oil filler cap and the hood. This means there's a big hole in the hood to fit the downdraft carb.
I designed and 3D printed two intake manifolds out of PLA to adapt an A14 to a pair of sidedraft SU carburettors, coated the 3D prints in a plaster of paris/sand mix, burnt them out in an oven, and cast them in aluminum, then sawed the casting into its separate pieces and milled the mounting faces of the intake manifolds flat and parallel (and the same height.)
There were a number of issues: one bit of the mold didn't fill so I had to weld it up, the way I made the 3D print with switchable plates to fit the two differently-handed carbs ended up leaving weird divots on the inside of the casting, and the top face of the castings don't have the detail I'd like, plus just pouring the plaster over the surface meant there were big air bubbles on the bottom sides of the top plates.
However, they slip right on the A14, they'll seal well, and they fit the SU's.

I also designed them with fuel injector bosses so if I want to go down that route I have a good start. (In the long term I'll get a Hayabusa throttle body set and cast another pair of these with diverging rather than converging ducts to fit the Haya spacing.)
I hope the included pictures come through okay.

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  PLA_print.jpg (22.10 KB)


  rough_casting.jpg (39.94 KB)


  sawed_loose.jpg (36.82 KB)


  on_engine.jpg (33.05 KB)


  milled_and_drilled.jpg (39.12 KB)