I have heard the same thing as well, about the exhaust ports. Leaving a bit of a lip, where the header bolts on, will (allegedly) prevent the gases from back-flowing. (Allegedly.)
I've seen them leave a small lip, and even an additional "raised, flat floor", in the exhaust port. Kind of looks like a "D", sitting on its face.
Here's some pics of my port work. (Done by Goza, in Woodstock.) Unfortunately, none of the exhaust ports.
![](http://gafieroclub.org/pics/pip/dual_head_ports.JPG)
(Ignore the red circle.)
![](http://gafieroclub.org/pics/pip/Port_marked_(Medium).JPG)
And the intake. Ported by Darrell Morse. (No longer doing this, as far as I know.)
![](http://gafieroclub.org/pics/pip/Intake_to_head.JPG)
![](http://gafieroclub.org/pics/pip/Intake_top.JPG)