Get your build sheet so you can see which spring codes you have. The build sheet will give you a three-letter code which can be deciphered using an FSM to get the two-letter codes below. Or you may get lucky and be able to read the two-letter codes on the springs themselves. The spring rates are as follows.
LL - 3-1/8" free arch, load rating 405
LM - 5-5/8" free arch, load rating 605
LS - 6" free arch, load rating 675
LT - 7" free arch, load rating 755