So naturally aspirated. Well with zoomies on a non blown application will make your engine be the poorest performer at the track. The engine will be confused below 4500 rpm or so then clean out and act ok for a few thousand rpm then revert at another rpm higher again. Zoomies provide no help to the incoming air charge to the head and will not give the benefit of sharing exhaust pulses to aid the scavenging effect for the next cycle that a good working collector will. If the length is short it will also burn the hell out of your exhaust valves if you are persistant in trying to tune it that way.
A step pipe or non step, 4 in to one collector type is the only proven set up or a few variations of that for naturally aspirated 4 cycle engines.