I just did this over the weekend on my '48.
LMC is just re-selling Posie's Dual Flex Springs. You can get them cheaper through SPeedway motors.
I bought the shackle kit from Dennis Carpenter to complete the job.
http://www.posiesrodsandcustoms.com/...-installation/
this link tells you all you need to know.
It lowered my truck about 1 1/2", my old springs were pretty tired. Probably a full 3" from factory height. I like the look, but the ride is so. much. better.!