Then you're fooling yourself, as you'll gain probably 15% flow with a crossflow head, given the bigger valves and simply better flow across the head instead of in, turn 180, and out again.
And the most important thing that you need to make any bike-carb-based stupidity even begin to work is flow, thus you really need to focus on improving the flow - bike carbs are one third, the head and cam the second third and the tubular manifold with a high-flow exhaust you are fitting is the last third. You are fitting a tubular manifold, aren't you?
Plus with the crossflow you'll lose the heatsoak from the carbs being over the exhaust manifold, which is likely to deliver vapour-lock in traffic conditions, which will be funny.
Plus you'll be able to increase the manifold runner length, which will strengthen the torque curve, lower down allowing you to actually race to the red-line instead of bogging down in the mid-range.
After all, taking the head off an engine is a terribly complex job, which few people have under-taken successfully - far more complex than a quad-carb conversion....
