The convertible spare tire bracket is not usually spot welded - it is tack welded in place from the topside with a blob of weld every 1-1.5" or so.

At least for 1970

This is based on having a number of '70s, including a bracket that I removed along with part of the floorpan from a '70 'Cuda 340 convertible that was crashed/written off in 1973....