i need to replace the trunk floor in my cuda

If it was me I would get the whole trunk floor so it is 1 structure with all the unibody stampings correct , check out my thread on restoring an already restored car and you will see how we did my floor it is stronger to weld the new onto the rails instead of trying to infill with bits and pieces . It is easier as well really just cut wheel down the inner side of the extension seam and drill out the spot welds all around the floor then I drilled 3/8 holes in the new floor in the same pattern as the factory spot welds and we plug welded it in so it looks like spot welds after grinding the slag off .