For the sides I used a scrap piece of 1/2" steel plate about 4 " wide by 8" long that had a round edge as a dolly. The width of the plate allowed me to grip it, while holding it in place, close to the edge of the hole. I used a body hammer to form the curve. For the corners I used the round end of a ball peen hammer to slowly tap the edge to the correct size. A body dolly was moved around the edge when slowly, evenly forming the corners. Bending down the edges and using large radius corners maintained the stiffness in the floor. The angle iron on the edge of the transmission opening will increase the integrity of the floor.
