Mike
Done that many times, replacing the quadrant on a bare frame, but haven't done it with body and sheetmetal on top of the frame.
A '
fix' may be made by shearing off the rivet heads and punching out the remains, but under the car would be harder task, then drill out the holes and place grade 8 bolts and nuts to secure the new quadrant.
But..... a
repair is done better removing the splash shields, (body lift some is needed) to get real access to the part. Then drill into the rivet heads part way, then punch out, takes some work to get off the old part. After that, air hammer and torch to heat the new rivets red and set them, two persons are best, one to rivet and one to buck the rivet head.
Just did this quadrant over Thanksgiving on the '13 frame with helpers, grandson and a son-in-law.....good workers too, did the forged running board brackets first and then the quadrant rivets , purty good for beginners! (RV Anderson supplied the correct rivets, his fasteners are made to factory prints)