Trail beast, one should be able buy a heater core, that claims to fit perfectly and not have to do any work. Do we buy new homes with doors that have to be cut and fit to work? The box broke because I believed the vendor's claims of a perfect fit. As the tubes pushed through the opening, one did not fit and pulled the metal plate off, stripping the screw hole. As this is old fiberglass, it does not take much to damage it. Hope that helps with your understanding.
