My roadster right hand headlight was about 1-1/2 inches closer to the radiator than the left. I took off the brackets, made both the same shape, tweaked anything else I could think of and got the gap to 3/4 difference. Only noticeable if you told someone. I used some serious force on both guards without removing them, but could not get the gap closer. One fender is more crowned, the other more flat from accident damage and repairs long before I got the car.
I cheated by modifying the headlamp ball mounts slightly to gain another1/4 inch and now live with a half inch difference side to side. All this was 15 years ago, so I cannot recall all the details.
The real fix is to remove the left hand guard, strip the paint and wheel more crown into the shape to narrow the profile. This was too much trouble for a car I just want to drive and not show.
A few years ago my wife's 31 Tudor was hit on the right front. Insurance paid for a top restorer to repair it.
That fender is now noticeably higher than the left. Again a big job to reshape, and not something I am contemplating. The first thing that happens in an attempt to squeeze in more crown on a finished fender in two-pack is the paint will crack. On my roadster I split the edge wire in attempting this fix too.
Not very encouraging for you, but if the basic crown and width of each fender are not rhe same due to accidents and repair, no amount of adjustment of the underside mounting arms will fix things.
SAJ in NZ