Air box size was a constant battle and they got bigger through the years, no doubt the styling guys fought it tooth and nail. Take a look, All years of XS650 and about every other twin have a cross over tube between the boxes. At first it was outside the air filter? then I think starting in 74 they managed to get the tube on the engine side of the filters. That tube effectively doubles the air box size for these 360 firing twins. Mechanics hate them, and they were expensive to make.wheres the big air box an a 1975 xs650?
A K1200LT BMW shows the influence of early CAD design. the airbox is the weirdest looking, convoluted thing, sucking up every speck of space under the fuel tank and around the top frame tubes.