Modifying a pulsar one or similar.
Its designed better for flow and distribution than anything NMS or AVA or anyone else "back street garage" is going to come up with realistically as its had millions of pounds of development thrown at it.
Any of the companies listed above can only realistically do a "thats about right" kind of design.
Thats NOT having a go at them, clever blokes, just dont have the resources of someone like nissan in the first place.
Also a pular one is 50 quid secondhand!