coil spring codes?

I just acquired a 91 Aerostar XL (2wd). The Front Right Spring is broken and needs to be replaced, so I was searching an on-line wrecker. One of the criteria the wrecker's database requires is the "spring code". My choices for the front include "J", "K", "M", and "X".

Could someone tell me what these codes mean? And, how I would find out which one applies to my vehicle.

Thanks

je

on driver door post is manuf. label with spring code listed on it for front and rear.
example> FR, F is front spring code, R is rear spring code.