It says "3.08 and Up" Which I would assume means 3.08 and steeper ratios then?
Generally that's the case - but don't assume . . . verify. If you've never done a GM differential/ring/pinion install, I'd suggest having it hired out - or having an experienced friend help. There's one way to do it right, and about a hundred ways of doing it wrong.

I've had good luck with Randy's Ring & Pinon for obtaining parts. He has just about everything, and has a good website for hunting parts.