I don't think I want to adjust the header. It might have been able to be done tighter, but I don't have a steering column in the car yet so there might be reasons.
I really think some careful hammer blows to the inner fender would open that up quite a bit. And since this is the side where the motor rocks away (assuming there is any kind of squish to the motor mounts), the gap will only get better while it is running.