I had the same problem recently, with a new plate and drum. I decided to file the tabs on the plate instead of the notches in the drum. What I did was to put the plate in a vise with soft plastic jaws, with one tab sticking out horizontally. I gave the upper edge three swipes with a very fine small file, making sure the file was nice and square. I then moved the plate to the next tab and did the same, marking the plate near the filed tab with chalk. Tried the plate in the drum. No go, so I wiped off the chalk marks and flipped the plate to attack the other side of each tab. This routine had to be repeated two or three times, testing each time. Once done, it fit the drum with no backlash but slid easily in the notches.