[Kahuna]

I fully agree with Bruce, Ol Ron and others that the exhaust ports are not the problem some folks have professed. I was quite suprised at the smoothness of the internal exhaust passages from the factory. Henry did a good job, except at the end port exit; but that area can be filled either with a metal insert, or better, with a high-temp moldable material. Then ground, smoothed, etc. Tim, don't worry about the back pressure. You don't want any and anyone who tells you otherwise is blowing smoke.
Jim