There's a metal plate that the bolt goes through, holding the spring to the lower control arm. That plate will fit snugly around the coil's "tail." Which ever end that plate fits is the bottom of the spring.
-Brad
Brad, thanks for the reply. On my truck there are two of those plates for each spring, and they're identical; they can interchange from the top and bottom of the spring. The only difference is the one that holds the spring to the control arm has a nut welded on it and the one that holds the spring to the frame doesn't.
I found what I was looking for, though; the tighter loops go to the control arm. I looked through the builds of several '64-'66 trucks on Stovebolt, and found several pics to confirm. Thanks for your help, though!