Gotta tell you, if you have never used urethane suspension bushings be prepared to be suprised in a noticably rougher ride, maybe more performance but rougher. I have did several with them and none are as smooth as factory bushings, last muscle car was a chevelle and used PST graphite impregnated, it stops the squeaks of the pure urethane and seemed the best I have tried, none are cheap. PST | Car & Truck Suspension Parts | Performance Suspension
I had a buddy with a '67 vette with all Energy Suspension bushings and you needed a mouth piece to ride in the thing, sold the car it rode so rough, rode much smoother with factory rubber.