These are the specs for the "heavy duty" spring available for the MII:
INSIDE DIA.= 3.5 in.; BAR DIA.= 0.59 in.; FREE HEIGHT= 13.81 in.; SPRING RATE= 364 Lbs./In.; LOAD= 1561 Lbs.; LOAD HEIGHT= 9.5 in.; END 1= SQUARE; END 2= TANGENTIAL
...and the specs for the standard spring:
INSIDE DIA.= 3.51 in.; BAR DIA.= 0.58 in.; FREE HEIGHT= 13.94 in.; SPRING RATE= 317 Lbs./In.; LOAD= 1400 Lbs.; LOAD HEIGHT= 9.5 in.; END 1= SQUARE; END 2= TANGENTIAL
The heavy duty spring is Moog 8556 or TRW CS8556. The standard spring is Moog 8582 or TRW CS8582.