As one of the people running motorcycle carbs I will also say that replacing the 32/36 is much easier and for a mildly tuned A12 just fine.
Note when I bought my set up it came with a custom manifold that was professionally fabricated for a race car. As for tuning the carbs, they were fairly easy for me but keep in mind I have a lot of motorcycle racing experience. In the tech section you'll see my near stock GX motor made 73 rwhp with 39mm flat slides which considering the stock GX motors were rated at 83 hp at the flywheel is very good.
For a road car with twin carbs I would go with a pair of 38mm CV style carbs.

Tom