We have 1" torsion bars on our 70 RR with a stroked 400 (452) with Edelbrock heads and a Weiand tunnel ram. I do not feel they are too harsh. Have been thinking adjustable shocks stiff on compression a little softer on rebound will go a long way to helping our oil pan survive (road race pan and have managed to dent it, of course, the car was stuck on top of a large rock at the time...). With your description of your friend's car with all iron engine get the spring rate up, go 1". I think our's are Mopar Performance.