Ok mate,
Quite an old car then, but even so...
Every radio system operates at a set frequency by using whats called 'crystals' inside them. Now by placing the whole radio unit in a dry freezer you will be freezing and breaking the crystal, forgoing the need for a 'code' as the radio doesn't need to authenticate itself with the car.
I have successfully done this with my car '51 307 as the person i bought it from forgot to mention that the radio in it didn't come with the car, so i froze it for a couple of hours and hey presto - working radio
Disclaimer - I will not be held responsible for any damage caused by mentioned process and my advice is purely taken from my personal experience.