I think you might wanna consider the basics before thinking about a blower. Banks offers this kit that consists of basic intake and exhaust mods. Looks like it includes cold air intake, headers and full exhaust. Not sure about price but a few thousand will not cover a supercharger.. Let alone install and tuning.
http://www.bankspower.com/System.cfm...amp;sysid=SC12
Supposed to be good for gains of +24 hp, +27 lb-ft torque and 2% better mileage. It would really compliment the increased breathing of the blower if he wanted to do that later. Lot's of other manufacturers offer intake and exhaust, I just ran upon this "system" from Banks. They've been around a long time but I can't comment on quality and I doubt it is cheap.
If he wants the supercharger, I'd recommend he take a look at whipple and kenne-bell. Both offer roots supercharger that would make an boatload of torque from the 6.0 liter. Here is the whipple.
http://www.whipplesuperchargers.com/...sp?ProdID=1136
and the kenne bell.
http://www.kennebell.net/supercharge...60/gm48-60.htm
Hope this helps.