Ring and pinion gears question?

Alright, I feel stupid for having to ask this, but i want a 3.73 in my 91 firebird (it's a 305 tbi that me and my bros work on, drum rear) could i just go on ebay and get a ring and pinion set up for like 50-100 bucks, and would that work, if so what size do i need, 7.5, 8.5, 100.54? And how hard will it be to put this in, does it have to be done by a professional. Thanks a lot for the help guys!
Jake

If it is a stock rear axle, you will probably need a 7.65" ring gear. You very well may also need a 3-series carrier, since the original ratio could easily be 2.73. A ring and pinion set doesn't have to be installed by a professional, but it does have to be installed professionally. You'll need a dial indicator and base, a new crush sleeve, some feeler gauges, layout dye, an inch-pound torque wrench, and access to a surface grinder or a source of assorted pinion shims.

Other than that, it's pretty standard stuff.

Man, thanks a lot for the info. That is something that I have never done before, and looks like it's going to stay that way, lol. Would it be better to just buy a whole locker assembly to put in there?
Jake