There is a fairly simple answer to your inquiry.
B&M (Now Holley-Weiand) builds a belt driven mini supercharger that will fit under most GM hoods. It was designed to add 100 horsepower to a stock 350 engine, although real world results seem to be in the 40-60% increase.
Anyway you look at it, these mini blowers make cheap horsepower. Depending upon the compression that your engine has, you adjust the amount of boost by changing pulleys.
My blower came with pulleys to make 3 pounds boost. I have built a blower motor with forged blower pistons, good rods and rod bolts, a blower cam shaft, and a good hot ignition and aluminum heads. Because of the parts that I am using, I have bumped the boost up around 10 pounds, and Dyno 2000 says that I am making over 530 horses and 460 ft/lbs.
Well, I don't race dynos, but it does go like stink. ( I accidentally shut down a pal's 11 second Corvette).
There have been a bunch of small block chevy blowers on Ebay this month...Many went for under $800, most went for under $1300. The mini blower gives a quick and hefty horsepower/torque boost to mild engines.
People will tell you about the need for forged pistons, big rods, beefy bottom ends, etc. but the truth is that the small blowers were designed specifically for stock engines, and if you keep the RPM at a reasonable limit, there is no reason why the engine wouldn't perform as designed.
If you can change an intake manifold, you can install one of these mini blowers. The hardest part is the throttle linkage and on a cable type, it is not an issue.
For more info, go to www.Holley.com
and click on superchargers or weiand then superchargers.