Leaf Spring Rate Capacity - '65 vs. '86

[focusedontheprize]

Hey,

Trying to find out a little more information on this subject or if anyone else has ran into this before. I am working to build a stout 1965 Chevy C30 work truck that will have a flatbed and a gooseneck down the road.

I have a set of rear leaf springs (9/1 leaf spring pack) that came out of a 1986 GMC 3500 donor truck. That truck will also provide a 14FF that will be going underneath the '65.

I took some measurements of the '86 springs and compared them to my '65 springs, however I am trying to find out which pair has the highest spring rate capacity and just the better overall springs. According to RockAuto, the '86 springs (which are the 4 5/8" pack thickness) have a 4500lb per spring rating. I unfortunately cannot find any information on the '65.

Does anyone have an insight or information on the rear springs for a '65 Chevy C30? They measured to be a 4 3/8" pack thickness and were a 7/5 spring pack.