I have a 49 GMC and I bought a kit from Macgyvers Rod & Custom
http://rodandcustom.ca/ that included everything from shackles, u bolts, springs, shocks that mounts to the original holes int he chassis. I bought it from them as they are cheaper than trying to get something to me from the US as I am in Canada. My other option was a company called Standens, but they only make the springs...no kit.
http://www.standens.com/