As one of the responses said already, you need to be sure its the shackles or the shackle bracket? (could be both?) My experience from doing the shackle brackets on my '92 is that the tasks involved are difficult and time consuming. My truck has alot of rust on the entire chassis and undercarriage. The 2 shackle bolts were very difficult. Getting the nuts loose and off wasn't too bad. Alot of PB blaster, some heat and breaker bar. The tough part was getting the bolts to "slide out." Remember, the bolts are surrounded by a rubber grommet, and all the rust inside (that you can't see) made it very difficult to extract them. I don't have cutting torches, if you do, it would make the job much easier. Remember though you still have to get the bolt out of the rubber and that's very hard even if you cut the head off the bolts.
The shackle brackets, if you have to replace them, are rivited on. Removing them is time consuming. If you have cutting torch it's obviously easier then drilling them out.