The lower A arm bushings are basically the only rubber in the front suspension besides the upper strut mount and the swaybar. These are the two that if you use poly will make for a very firm ride, excellent for handling, not so good for a luxurious ride or quiet cabin. The large one at the rear in the aluminum bracket is made to give quite a bit when you hit a bump, the poly just doesn't give much at all. That bushing has a large gap built into the center of it, with a plastic ring insert in that space, the poly is solid poly. The front bushing doesn't give much at all, in rubber or poly, which is why I think you could use poly for the front and OEM for the rear, but others may argue that that is not a good idea. Visualize the arm when you hit a bump, the arm wants to pivot back about the front bushing and the rear of the arm wants to move toward the center of the car, stop the arm from rotating and you get a much more firm "hit" when you experience a pothole, etc. The poly in the rear position makes the whole arm virtually rigidly mounted (though still allowing up and down, of course), which means your alignment stays true no matter what crazy stunt you are pulling, but the luxury is gone. Love/hate tradeoff.
Charles
