I've put in lots of MII systems with Heidt's being just one of the many brands.... As long as it's the "good stuff" with DOM or Moly round tubing for the arms, forged spindles, and big brakes they work fine on a big car. As Charlie mentioned, measure, measure, measure, check for level and square a few times, then measure some more!!! On a big car, I would also suggest getting the sway bar option on the front end. I've never had any problem with the GM 11" on the front, but to qualify that I bit I run discs on the rear most of the time, too. Getting the new crossmember in position, squared with the rails, and set at the correct angle is critical to having a good handling car!!!!!