[Gas_Pumps]

That gear is the starter ring gear on what looks to be the flex plate or "flywheel" of an automatic transmission. At least it doesn't look like you can use Flintstone foot brakes like some I've seen. Good Luck. I have a '65 vert, same color. Had right front damage, but fortunately no rust.

 

[ylexot]

Floor pans are not an unusual thing to replace in a mustang, let alone a rag top. I would only be worried if the frame rails were severely damaged by rust. Your inner rockers look good from what I could see. Check your torque boxes for punch through rust as well. Fortunately for me, I only had to replace the driver's front and passenger rear pans in my vert. Keep this in mind- nobody makes a replacement convertible seat riser (what your seats sit on) so you will have to reuse the old one if you go with full length pans. Do you have the under body stiffener plate? It bolts underneath the seat riser under the car across the drive shaft tunnel.