I bought and drove my 71 Z car for one year, Last year could not drive it. Could not pass emissions. Pulled the engine (bad rings) last week to swap with other engine that I rebuilt two years ago. When I pulled the engine I noticed that frame section under the swaybar had rust damage. The guy that owned the car before me, had someone re-enforce the frame with 12" L shape metal plates and bolted it back together. Can a frame shop repair or weld these two sections with the metal plates. And could this cause the vibration I get when I accelerate over 40 mph, This didn't happen until a year ago, one month after I had the tranny serviced. Some times it rides smooth as glass if increase the speed to 70 mph but not all the time, If I reduce the speed slightly under 70 the vibration starts again. Any clues about vibration, I put bearing in and all U's on the drive and half shafts are new. What the verdict on the frame ????