I just used the auto rust technicians subframe connectors on my '72 charger, and didn't have to cut anything on the car at all. They're 2x2, but I'd think you'd get more rigidity from a solid, uncut 2x2 than you would from a cut 2x3... I did have to modify the connectors slightly (literally a 5-minute modification) because they were a bit long, but I think my car is a mutant


Also, I've heard a lot of people recommend torque boxes, and a.r.t. carries those as well, but I have no idea on that one. My car apparently came with them stock, or had them added before I got it, so I've never given it much thought.