I will be honest, I don't know that a 275 tire can be tucked up under a malibu without some work. I have seen a few cars with 275/60's on them but the car is up in the air. You have to get the back spacing just right and cut a lot of the fender lip off. Even go as far as notching the frame rail. I have run the 255's on mine for that reason. Based on the pictures, I would guess your wheels are 3.5" backspacing and won't work for what you want to do. The front and rear springs are different styles, so they are not the same and no, they don't have to be the same spring rate. A lot of times, the front springs are heavier to hold the concentrated weight of the engine. Front springs are a little easier as they are a straight wound coil, so you can jut trim a coil off to lower the car. The rears are smaller coils at the ends to fit the spring seat, so you can't just cut them.