Leaf spring length

[RodnRudy]

My 77 SWB C10 Silverado has a weak spring on the pass. side. I went to the local spring shop and they measured my springs at 56" long, 26" from the front spring eylet to the center bolt, 30" from rear spring eye to the center bolt. I've been told the spring on a 1/2 ton SWB is 52" long and 56" for the LWB 1/2 ton. This is a factory SWB frame and the hangers are riveted to the frame, haven't been moved, and the frame hasn't been shortened. The spring shop can make me new ones no problem but I'm curious if any other guys out there have the same length spring on their SWB 1/2 ton. Could one order the heavier springs back in the day? It is a puzzlement to me. I hope Keith Sizemore, the square body guru will chime in