Need some help in possibly identifying the production date of my engine. I know the engine was installed in my Shelby Mustang in 1979. What happened to the original 428 is unknown other than the owner wanted more horsepower than stock. I’ve taken a photo of the pad adjacent to the
oil filter on the driver side but having difficulty in deciphering that one digit to the left of the H. Any help would be appreciated. The heads are iron and the lifters are solid, not hydraulic.