[462ron]

Hi, to remove those vertical ribs you need to remove the big speaker first. Be careful in doing so as there is a wooden cone in front of the speaker that will rip your speaker cone if allowed to come in contact. On my set, I removed the 2 nut and bolts while keeping the speaker pulled back from the front and slowly lifting and tilting the speaker until it came out. Then you need to remove several wood screws all around the perimeter of the speaker board. That board along with the 3 acoustic resonators and grille cloth will come out then you will see the screws that hold those ribs and remove them!

Ron