Need a box shaped nosebowl

I have an experimental Bushcaddy with a Lyc O-235. I also have the
standard ACS nosebowl for a lyc: http://www.aircraftspruce.com/catalog/appages/mc3a.php

My exhaust is a slightly modified Powerflow system. I have just
discovered I can't use my nosebowl because it is too rounded on the
bottom. The top is fine but the bottom is basically a crescent shape
from side to side. To accomodate the exhaust pipes and collector box
from the powerflow sytem I need something with a more rectangular or
boxy shape on the bottom. As an example a powerflow system will fit
in a Glastar Sportsman but their colw costs $1200. Any thoughts or
ideas??? Any kits you can think of that have such a shape to the
noebowl where perhaps I could buy that component??

Thanks. Don...