When you say piston, do you mean body or shaft?
Body goes to frame mount, shaft goes to draglink.
And yes, as said it can go either way and function just fine. But less weight on the steering component the better. It's minimal maybe, but in theory it seems better to mount the heavy end to the stationary mount. At least to me...;D
Also, not sure if it would happen, but having the big end able to move up and down could be more likely to run into interference with some other component, depending on how the overall setup is in front of any given Bronco.
Paul