Maybe the casting is a bit different on your motor, I do not remember if my 4.3L engine was the same as yours.
On an unrelated note, I always thought the circulating pump bolts were kinda weird anyway, as they were asymmetric. However, compared to the Ford circulating pumps, the SBC circulating pumps were a breeze to change.
You will want to put some Permatex Aviation on the circulating pump bolts to seal them from water.
