Like Jerry says the OEM rear should have a tag or you can turn the axle one turn and count the pinion yoke turns to get close, then compare to the OEM ratios from that year to dial in what you have. For your ratio you need to plug in your rear tire diameter and final tranny drive ratio, then pick your optimum cruise speed. Here's a link to an easy calculator that you can use RICHMOND Street Performance Calculator On mine I run 1995 at 70mph, which works pretty good for me but you need to look at your power band (torque curve) on the engine, and what your speed range will be. Some of the newer OEM's are only turning around 1600 at highway speeds to push economy, but you have to stay in your power band or it will be going in & out of OD all the time. I like positraction, but for your Buick cruiser I would not think you really need it unless you're planning for winter driving? Not sure of the weight, but I'd say you'll shave off 150 to 200#, and with that heavy Buick that helps.