Leaf Spring info/help?

Hello I am a newb. Right now I am in the market for purchasing new leaf springs and shackles for my 71 dodge dart swinger. Swapping out he 7 1/2 for a 8 1/4 with an Auburn limited slip :) As i was looking around I found the Mopar performance competition leaf spring and noticed there was a left and right but one was more money? probably a dumb question (But I don't know a whole lot) is there a difference in the left from right? and If you guys have any recommendations would be appreciated.