A. This topic in Virago Tech answers this question very well,
as does this one.
Comments: There are two makers of 2 into 1 manifolds for the Virago that I know of.
One is a guy I know only as "Hootenany Gizmo" who makes them to fit any carb you want to use, and to exit wherever you like (left or right side of engine). His prices are the lowest of the two, by far.
The other one is KJS Motorcycle Works. There are some issues with the the manifold from KJS Motorcycle Works, that I have been told about by Virago Tech regulars that have purchased one, and they include; A poor quality air intake and air cleaner, clearance issues on bikes with dual petcocks, and also issues with the carburetors that KJS supplies after you send them both of your stock carburetors. Apparently the consensus is that should you buy a KJS manifold, keep your own carbs and pay the extra that they charge for that option.
Additional Information: You can read about the single intake experiments that Mac McCurdy did on his bike at his Dr. Piston's Tech Page web site. You can write to the maker of the single carb intakes at the email address that I have linked with his name above. My personal recommendation is to see if Hootenany can make you one prior to using the KJS, simply because of the issues I've outlined above.