I had a Clarence Lee engine book..Vol. III. Can't remember the name, I gave it to a guy. That's where I learned about degrees of duration and all that.

All I do is alter the timing. I looked at the link you provided and I have to say I have never had anything but disappointment from removing metal from the inside of the engine. This increases the volume of the case, and that is bad. The piston can only displace a certain volume on the downstroke..if you increase the volume of the case you can't get a full charge into the combustion chamber and the charge velocity goes down as well.

The main drawback to altering the durations of the engine is then you have to use a tuned exhaust. Most people looking to increase performance already run tuned exhaust since that's the easiest way to get power, so that may not be a problem.

I've done a bunch of engines and only had 2 that I made worse..both of them were porting changes that increased the case volume.