what size torsion bars should I buy?

Running 1.03" with a small block in a '74 Duster with Bilstein shocks. It rides well, but you'll definitely notice any holes or bumps in the road especially with low profile tires. You'll hit those obstacles and you'll hear the "BANG" permeate throughout the car, but that could be because I have the front suspension set too low. It does handle better though. I'm still dialing in the suspension.