Help on my 1964 4 speed swap

The sheet metal is spotwelded to the Trans cross member. You will need to be careful when cutting or have a buddy who knows how to cut around the laminated steel sheet where it is welded onto the unibody frame to help you out.

You can get a nice Blair spotweld cutter to put on a drill to cut out those spot welds so that the panel you are cutting out of the floor removes cleanly from the cross member.

Mark the cross member on the topside of the sheet metal floor inside the car with a paint pen or sharpie, and cut around your marks.