As long as you have it tuned and jetted correctly, it really doesn't matter. Carbs are used in both orientations with no real gain or lose either way. On the 292 dyno tests that tlowe did recently, the carbs were on the intake with the shafts perpendicular to the engine because the dyno throttle controls work front to back , but when placed in the vehicle, they will need to be turned parallel to the engine because of throttle cable routing. So its probably preference more than anything.
