Since the Venture/VMAX motors are also 70 degree V's with four valve heads and of similar vintage to the Vision, I reasoned that the same team probably designed these motors and the Vision's, and that two Venture carbs might work and be simpler to tune as they are CV carbs turned sideways. I bought a whole intake setup for a Venture (vintage unknown), everything from the rubber intake manifolds to the air box at a swap meet to experiment. I stripped down the carbs to use the main pair that connect directly to the throttle cable.
So far, I've mocked this up on the parts bike. Using the Venture carb manifolds rotated so that the oval ports lines up with the oval ports in the Vision heads, this looks like it's going to work while retaining the air box. I'll need to make up an adapter for the misalignment of the manifold and the threaded holes in the Vision heads and cut back some of the manifold for bolt clearance. The choke cable looks like it will work, but I need to make a different throttle cable mount to clear the air box. The bottom of the airbox is at about the right elevation for the Venture rubber velocity stacks, but will need to be modified for the different carb spacing using either the bottom of the Venture air box or some aluminum plate.