The Mauser rifles manufactured by Carl Gustav had the year of manufacture on the top of the chamber, under the manufacturer's roll mark. If this is faded on your rifle, examination with a magnifying glass or the use of a product like White Out may be necessary to make these markings legible.
If this does not work for you, you can go to www.surplusrifle.com, and additional resources there or people affiliated with that website may be able to provide you with assistance.
The Mauser rifles manufactured by Carl Gustav had the year of manufacture on the top of the chamber, under the manufacturer's roll mark. If this is faded on your rifle, examination with a magnifying glass or the use of a product like White Out may be necessary to make these markings legible.