As I understand it, peak boost depends on alot of factors. The 12 psi figure quoted in that article is suspect to me. Here's my train of thought based on experience. My '99 GTP made 7 psi peak boost as it came from the factory. I know this because I installed my aftermarket gauges, to include a boost/vacuum gauge before I started modding the car (the factory gauge in those cars is just a segmented bar graph with no numbers). The stock pulley on that s/c (roots type Eaton s/c, by the way) was 3.8" in diameter. When I swapped to a 3.4" pulley, the boost peaked at 10.5 psi.
Here's where it gets interesting. When I installed a 3" cat-back exhaust, with the same 3.4" pulley, my max boost dropped to 9 psi. At first I was puzzled, and thought something was wrong. However, dyno tests and 1/4 mile runs proved that I was making MORE power with less boost. The reasoning behind this is that the exhaust was more efficiently getting the spent gases out of the combustion chambers. So the cylinders were more devoid of air at the beginning of the intake stroke, and they could thus suck more air in from the manifold on each stroke. The supercharger was pumping the same volume of air into the manifold, but the heads were able to swallow more of that air than they had before the exhaust modificatoin. This is what lowered the overall manifold air pressure (boost). So, overall, my engine was moving more air/fuel even though my max boost was lower.
Now, when I swapped in my 3.25" or 3.0" pullies for track use, my max boost would shoot up to the 13.5 psi range. Up there, I absolutely had to run race gas and bump up my fuel pressure in order to avoid spark knock and the dreaded knock retard. I could have controlled it with a modified PCM, which contained more performance-oriented fuel maps, but that's another topic.
Anyhow, that is my train of thought. A higher max boost doesn't necessarily equate to better performance. Sometimes, it can mean quite the opposite.
As for the 12 psi figure, my best guess is that maybe that supercharger, installed on that motor, but with a pulley sized to spin the s/c at the max RPM recommended by Eaton may yield 12 psi of boost. But unless the compression ratio on that motor is really low, there is an intercooler in there, or GM programs the ECM to just dump loads of gas into the mix to lower combustion chamber temps, you would have heaping loads of knock retard.
As for the differences in engine internals, I would expect dished hyperutectic-coated pistons just as in the L67 (GTP motor). The dished pistons lower the compression ratio, and the coating makes a good compromise between cheap cast pistons and far more expensive (and in some ways problematic) forged pistons. Ironically enough, it's the hyperutectic coating that makes the pistons in L67 engines so brittle, and thus shatter-prone under severe spark knock conditions! I'd be surprised if much else changes besides the pistons. Ecotec motors are built to take a beating as-is.
Now, the turbo vs. roots type blower vs. CSC argument is a whole other issue. Personally, I'm in the [unpopular] roots camp, but that can be argued another time.
