I need to replace the seat risor in my 1930 CCPU. The old seat risor is secured in place with machine screws & nuts. Is this correct? I would assume since the floor plan is secured by rivets, that the seat risor should also be riveted in place. In checking rivets available, I am not able to locate rivets specific for this purpose. If the seat risor is to be riveted, what is the size of rivets needed?