I've been doing research (since my 98 F150 busted a leaf spring). I was going to do helper springs, but now that I have to buy springs I was just going to get some from the F250LD. What is the real difference between the codes? I've found codes for the F150 ranging from A-P and codes for the F250 ranging from 1-4.

First question... are the 1-4 codes for the F250LD or the HD?
Second question... I found a reference for the different codes, but they all list the same basic part number and rate. What's the real difference?