if a local shop has the other spring check to see if it would work, I have personally experienced auto part places giving the wrong parts even when they have the correct info.
perfect example is the first time I did the front brakes on me 89 chevy R2500 crew cab, I went in to the store and told them that year make and model, they gave me the brake pads, I got home tore apart on front brake and then found out that the pads they gave me where not what was on the truck(but they where the correct pads for my dads 94 chevy 1/2ton pickup), so with the pads from the truck went back to the store and they looked at all the ones their system said would fit my truck and none of them where right, until I told them to look under 86 chevy 1-ton pickup then they found pads that were identical to what my 89 had.
so maybe the 9.5 in brake spring will work despite being supposedly only for the smaller brakes.
There should also be trucks with the same size differential and brakes that might have the correct spring, or there is a new design so it would fit but not look the same.