There were several leaf packs that could have been used on your car. You can look in a '66 parts book to see which ones. Generally a spring that has been cycled excessively or overloaded is not really a good choice for continued use. If you do get used, then look 'em over for signs of failure, then load them up (stand on 'em is one way - but do hold on to something get on and off!) and measure the deflection. Then calculate the spring rate of each. If left and right are not the same - one or both is worn out. If they are OK, you can rebuild with new interleafs and bushings.
This company has some information posted
http://www.stengelbros.com/DodgeCarLeafSprings.htm the link was posted in this thread
https://board.moparts.org/ubbthreads/showflat.php?Number=7193764which you may find some it helpful
