On 95% of leaf sprung Jeeps the shackles were mounted at the front. However, mounting shackles at the back is commonly referred to as a "shackle reversal". This is a common modification in the US with TJs and CJs and while debate is still ongoing of its advantages and disadvantages, it is perhaps best suited for a hardcore offroad rig.
Detailed info on following articles:
Pros and Cons of Shackle Reversal - - Jeep at Off-Road.com