I wasn't being a smart ***. ( well maybe a little ) Unless your truck is missing it's rear springs, why not just use the originals ?
UHHH Not taking up for Mr E-wood here, but he pretty much knows his ****. I would do exactly as he says.JMHO
There are numerous possibilities, but the question is, what are you wanting to accomplish with the replacement springs? Lowering the truck, improving the ride or restoring the original load capacity? If lowering a bit and improving the ride is the goal, I’d look at S-10/S-15 springs and frame hangers/shackles. I did that for my ‘54 GMC and was quite pleased with the outcome. In order to keep the axle centered (fore/aft) it wil probabl6 be necessary to change the position of the hangers and shackles from their original locations. There are other leaf spring setups that are adaptable as well as having new springs made by a spring shop that will fit existing mounting points. Ray