[jmmm229]

The plywood floor, though hardwood, flexes and moves with the body and chassis. Not sure if thats its purpose, but in my thinking as a structural repair tech, replacing it with more rigid material may or may not cause damage elsewhere on the body when the vehicle flexes and twists. 70's Camaros were notorious for this where the 1/4 panel was brazed into the roof skin from Fisher Body when you add a big powerplant and/or a roll cage or subframe connectors.