If the frame has rust on top, you may not be able to just patch it up and last for very long. The quickest and sure way of repairing it, is to find another donor frame, and move everything over. That is a very doable job, but time intensive. If you try to weld it with the body in place you run a high risk of the body catching fire. Once fiberglass ignites, it can be very bad. You might take it to Corvettes of Houston on the north side and have them look at it. They might be able give you a better idea what you are up against. Or if you know of another place that has a specialty in Corvettes. Hope things go well for you! Let us know how it goes.
Bill