go turbo and you'll be able to find lots of stuff.
but if you really want a supercharger system I think these guys make a kit for the M20, or at least they did http://www.albrex.com/flash.html
^^^^^So not worth it IMO...with the DASC being the only bolt-on kit for the m42 and its crazy price tag (something like 4kUSD) and ONLY getting a mere 190-200ish hp at the crank..m50 swap has 190hp stock (and more weight yes i know) but HP/$$ wise its much better. A s52 would be even better.....
Turbo is just better bang for the buck, and you get more power.
its not always about bang for the buck and more power, he has his reasons why he is interested in a SC build, and I agree with him. Yes you may be able to make cheaper and a bit more power with a turbo, but the SC kit will provide constant power through out the power band. unless your hitting a twin turbo on a inline 6 its hard to get a system that will boost from 500rpm to 8000rpm. a well built SC kit will provide more power over the entire powerband wich can result in more power overall because there is no lag time.
S/C takes power to make power. Couple that with belt issues, after cooling issues, space issues. It's much easier and cheaper to make a well designed turbo system then a custom S/C kit.
And I don't know what you're talking about 'random power' of turbos.. if you have someone properly match all the parts of a turbo kit up to your power goal you'll have almost an equal power band as a S/C setup.
New turbo technology has simply come a long way to think that turbo system have to be peaky in nature. That and there are too many people that just throw on GT40's.
Modern ball bearing turbo + electronic PWM boost controller + very linear boost and power levels.