Be careful! The 73-76 A-body uses a different bar than the 67-72, the 73 up bar goes through the K-member verse being mounted in front of it.
Bigger is necessarily better. Everything has to be in balance. Just for something to think about. More roll stifness in the front (i.e., bigger bar) will reduce under steer (plowing of the front end) at the expense of increasing oversteer (the rear end comming around). A stiffer bar in the back does the opposite.