Im not sure if this is the correct place to ask this but here goes. I've got a 1970 Cutlass supreme that came out factory with a 350 and I'm replacing that with a 455. The question is I'm replacing the rear coil springs in it and I'm not quite sure which ones to use, I see the ones for a 455 but also see the 442 springs. Which is the correct and what is the difference?

 

Check out the Chassis Service Manual it will show you specific spring rates. You should also define what your trying to accomplish as far as handling goes and if you want to lower it some. I have a 71 442 and had PST replacement springs and it handled and rode ok, I then switched SC&C front and rear coil spring and it handles even better. A 540-660 lbs front and 137 lbs rear would work well too.