Conversation Between ATS Junior and Blakshukvw

Junior, I have an 03 excursion 6.0 4x4. I need to replace the og springs. I'd like to gain 4 to 5" of lift. I'm interested in x codes for the front for sure. For the rear I'm uncertain. I've been told to use b codes or even modded b codes. What are the differences between b codes and c codes?