I had almost identical rust on one side of my ute. But by some sort of miracle, I was visiting a panel beater mate and I noticed he had the replacement panel- original from nissan in 1976 hanging up on his wall as a decoration. It turns out, a cusstomer of his from '76 had crashed his ute and ordered the part, but never picked it up. Meanwhile I had seen the panel a million times and nevr thought twice about it untill I was really stressed out about trying to find one!
Its not cheating- how else are you supposed to fix it? unless you take a crash course in panel beating