As far as I know, there is not difference in the numbers on the rockers. They may be difference production year numbers, or just different replacement parts numbers.
It's a 1977 OPEL Manta S, the car that OPEL released to compete with the Ford Capri in the 70s. But yes, It looks like a Chevrolet Monza!
My favorite car, very reliable, fun, comfortable...
Some photos with my latest OPEL Insignia Grand Sport from 2018 :
