The short answer is a lot things! But to be more helpful, its really a balance of all your suspension components and how they work together. If you're staying with stock torsion bars & rear springs, then you likely don't want to go to the largest sway bars available, if you're beefing up your cars springs you'll likely want to go to larger sway bars to match. Stock these cars that came with 7/8" sway bars on front (believe R/T cars came with heavier 1" front bars?) and 3/4" on back. So that would probably be a good starting point. Most of what I have read says that these cars need larger bars with better springs and radial tires so most folks run front bars 1 - 1.25" on front and either 3/4 or 7/8" on back. Some rear sway bars are adjustable so you can put them on and change the bar mounting holes to where you like the way the car handles. For my 73 small block Barracuda, I'm going to be installing .96 T bars and heavier rear springs (haven't decided yet) along with better shocks (either Edelbrocks or Bilsteins), a stock 3/4" rear sway bar and either a stock 7/8" front sway bar or a 1 1/8" Hellwig bar. So the answer is it depends on what else you're changing suspension-wise. I didn't even mention tires which bigger wider more grippy tires will also be part of the mix.
Later, Jim
