I agree, properly braced, generally using 1" square tube fully welded, tied in at the bolting points a well built fiberglass body is probably stronger than the original steel with wood bracing. You can also supplement the bracing to the extent of a roll cage, but will sacrifice room. Shop for a quality, hand laid glass body, with coremat panels in the floor, and perhaps the roof(?), and pay particular attention to the quality of the bracing.