way i made it easy for me.... what HP do you want ? get that, then it nail's down the snail's and you dont have a few hundred to go through, just a couple.
easiest way i did it was horsepowerinabox.com they have turbo's and HP rating, Flange spec, then i went off onto google and forum and read up on applications, and what else is needed to run the turbo.
but yeah once you work out your HP you want, its much more simple