Sorry, it's going to be difficult to determine the year of manufacture without a serial number.
These were made by Cor-tek in Korea, and outside of Korean Epi models, very few brands or examples have serial numbers.
Cor-tek produced limited numbers of base model EG Grecos in the mid to late 1980's.
There is a Made in Korea guitar thread with a Cort Greco example posted here:
If you post your pics to that thread as well, there is a better chance someone who has more info will respond some day.