You might want to skip revolver shackles alltogether and go with a set of Downey cantilever shackles. I believe the price is the same but the Downey's are built tough.
I have a set on the rear with 4"soft springs and the ride is awesome, on highway or offroad. And I no longer feel washboard roads anymore at all. Now if I could figure out how to put a pair on the front of my 83 toy truck.
