Please measure the diameter and thickness of your balancer. It looks like a smaller diameter than i had on my 455 Olds. Mine, if I remember correctly, covered at least half of each of the lower two mounting holes. It's possible that a balancer swap would solve the issue. I think if you try to mill a recess in the mount you may run into interference issues with those lower bolts. I think on mine the lower two may even have been recessed allen-head bolts. Now I have to see if I can find that old mount...............