Devil's Advocate but isn't the whole point of customizing the transformation of one type of vehicle into another? Otherwise you are just "enhancing" the bike's normal tendencies.
Example; my bike- not a custom. I
enhanced the bike's stock nature by adding rearsets, brake lines, suspension bits, etc.
Example; GM's bike- not a custom. He
enhanced the bike's nature by adding more chrome, etc.
Example; This ugly fucking 'Busa- total custom. He took a crotch rocket/potential drag bike and turned it into a blvd cruiser. Not my cup of tea but you cannot deny that it's a custom bike.
Besides, who made the rule that all 'Busas have to be made into "drag bikes" or super sport tourers to be acceptable?