Wow! What a can of worms... A "triangulated" four-link similar to what GM and Ford used will work on the street even with Heim ends. This is one of the most popular types of rear set-ups used by street rodders because it requires no panhard bar, eliminates binding, and provides a very good ride and good handling. Several pro shops use them, kits are available, or you can make your own, but... If you are going to flog this beast at the drag strip on weekends, this is not the set-up you want.

Pro Stock drag cars use unequal length parallel four-bar systems. This system uses bars that, when viewed from above, are parallel from side to side. When viewed from the side, the top and bottom bars are not the same length and are usually not parallel with each other. These are great for straight-line acceleration because by adjusting the mounting points of the links (they usually have multiple mounting holes) the "instant center" can be moved up or down which changes the amount of weight transfer that takes place under acceleration. These systems, however, are not good for the street because they bind terribly whenever the car tries to lean over in a corner. Eventually the brackets, the bars, or the rear axle housing will fatigue and fail.

You could use a parallel four-bar system with all four links the same length. In this system all the bars are parallel to each other whether viewed from top or side. This is the easiest of the four-bar systems to set up, but it provides absolutely no lift whatsoever under acceleration. It holds the rear axle in a neutral attitude regardless of its travel up or down. This system probably will not put those 500 ft-lbs of torque to the ground very well.

You could use a sort of "hybrid mix" of these two systems. Make a standard parallel system with all four bars the same length, but with multiple mounting holes. You could then adjust the mounting points of the bars to give you good "bite" when you go to the strip. Just make sure when you hit the street that all the bars are in a parallel attitude.

Your simplest, easiest, and least expensive option would be to stick with the leaf springs and put some "slapper" style traction bars under them. Lift is adjused by changing the snubber height and experimenting with the length of the leaves in the springs. With this system you don't have to crawl under the car and change a bunch of stuff every time you want to go to the races; it's always ready.