Engine decking issue(help)

Is there a possiblity i can just mill it doen myself with a 90 degree die grinder with a 60-80 grit sanding disc? Just looking at my options right now.
I am going to try and mill the oil pump a little at my work shhhh lol
But as for the main bolt or stud i contacted them about the issue and sent picture. Im not going to rely on them of course but i would rather not leave the washer off. Kind of at a stand still here. Dont want to go back to my machinist cause he takes long to do anything

Also rusty you have never ran into this problem before?