I had 3” on my 69...did have slight clearance issues back there where it went over the axle with considerable suspension travel. I put some Airlift airbags inside the rear coils to limit the travel and took care of that, not to mention improved controlling the sway on that big dude. It was a 44000 mile car all stock 430 with just a tuned Quadrajet ignition and the 3” exhaust that went a best of 15.01 driven to the track on a hot day That was one of the best cars I had ..lots of options a d ran great