Please forgive the inconsistent camera angle, but here's the head with the customer exhaust ports. The chambers haven't been addressed on this casting yet, so you're not looking at some Endyn combustion chamber tricks here.
Viewing through the exhaust port, it's easy to see the additional area to the sides that's gained by widening the floor at the short turn radius of each bowl. A discerning eye might also see the amount of radius that's been ground into the exhaust port valve seats, in anticipation of the upcoming valve job. The intake port's seats have also been transitioned from the bowls with only the 45 degree seat surface remaining. It's obvious that, whoever did this work either knew what seat configuration was on tap, or he was a wise-ass....or both!