I am researching Weiand blowers heavily myself, a 142 for a 334 and/or 6-71 for a 388. I think you gave me some advice about the stroked 305?! That isn't the blower motor, but I have another 305 sittin in the corner as well. Anyway, I love the 177, right around 2k in price and gives you 40-55 percent over stock. Plus, you don't need crazy mods to install them; most engines can handle their low boost pressure. I had similar questions when I planned on my build. The best place to go is www.weiand.com.
Click on the superchargers link, and then click on the general and technical information link. They had everything from what a blower does to how to pick a cam to ignitions and carbs. They also talk about compression levels, and what will work with what engines. For even more advice, look at the Holley and Weiand online catalog under the pages of "Air." They go into very good details about all aspects of using a blower. I believe that the Pro Street blowers (256 and lower) will clear a stock HEI housing, at least on a SBC. The ones that won't clear are the 6-71 and larger blowers. If it doesn't clear, the MSD short height Crab Cap distributor is an awesome replacement, especially with a Flying Magnet Crank Trigger. HTH!
P.S. A few weeks ago I saw a guy with an early 70's chevy truck at a car show. I noticed he had a 177 on his sbc. He had a Mallory ignition I think. We talked a while, and he loved it. I didn't really pay attention to the ignition because it wasn't a concern of mine until recently. He said the blower was good because it is very streetable, at least on his application, but it gave his truck nuts when he needed them. Good Luck.