OK, OK, we are both right, or sort of...
the gsxr carbs are pure side draft, 90 degs in relationship to the cyl block at least, their tilt angle comes from the fact that the cyl block itself is tilted.
cant remember the figure but I think that the block cyl was tilted by some 10 degs.
so its true that the slanted carb bowl line was meant to be horizontal, but when you think about all the braking/accelelration
that goes on, the sealing is not really depending on the line being horizontal.
I for one, have mounted both VM's (your type of carbs) and CR's at more than 10 degrees of overall tilt without problems (see my 10 degrees downdraft project thread), so that's why I was saying it will not be an issue, at least IMHO/experience.