I had a good file, but still, two hours with my arms over my head and stopping every few minutes to dial-caliper it to find the high spots made your word "drudgery" extremely appropriate. By the way, those high quality die-nuts are great, as opposed to those flimsey set screw housing Chinese dies that come in a tin-box set. One good M12 x 1.5 die-nut cost $17 at a machinery supply house but it was worth it.
Tom Kizer