I have both stock Model A's and also Hot Rods with Ford based suspension.
I do not have Pannard bars on my stock Model A's as I do not think I would gain much from them,
However, I do have them on my Hot Rods. and they really help, especially, if you are using cross steering or have longer than stock spring shackles.
Please note, Pannard bars and sway bars are two different things. Pannard bars are used to eliminate any side to side movement of the axle relative to the center line of the vehicle. This results in more positive steering. Sway bars are used to reduce the amount of "lean" of the vehicle during a turn. They can also be used to change the understeer or oversteer characteristics of the vehicle.
Chris W.