I don't "cook" in my small microwave oven, just heat things in it. BUt I bought my first one when they came out in the middle 70s. IT was ojne from Sears, and they really were called Radar Ranges. I tried it and returend it. If a dish is that old it must be that most olf kicrowave oven had less than 600 or less watts of power and if that is so, these dishes should possibly not be used in the modern, more powerful ovens.
I would call an electronics repair shop and ask them (not that anyone reoairs microwaves, everyhting is built to throw outw hen it breaks, but you never know, you might find an older guy who knows.