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I installed a power seat in my factory 71 Cutlass bucket seat car and welded in the outside factory bracket, but just welded a stud to the inside factory bracket, if I remember correctly. I also left the original stud in place.on the inside bracket. On the outside bracket I put a bolt down through the bracket into the original non power bolt hole in the floor. I'm going from my pictures and all this happened 26 years ago, so I'm a little foggy on the details. These pictures may confirm the results you've determined.