To expand on the correct but brief answer from luthier, the dial mounting pins on the back of the gen dials are placed for the omega movements which share the same footprint of the eta 28xx series of movements. The 21j movement has a different dial foot position. You could possibly cut off the dial feet and use dial dots or other means of attachment that we use for Rolex Franken projects, but this is not optimal. If you want to use a gen dial on an omega rep, you are better off getting one with an eta or eta one movement. Dial swap is easy then.
Ko67
