They will not work. Completely different cylinder heads. The WRX heads use a much larger OD for the cam seals. Look at them on the parts diagram and you will understand maybe. In any case the 25D doesn't need belt cover guides. You should check to ensure the cams turn freely. A damaged/contaminated cam journal could lead to such problems and may end one day in a broken cam.
The Gates stuff is junk. But you don't need to buy the parts from Subaru. Subaru doesn't actually make any of that stuff. Mitsuboshi, NTN, NSK, Koyo, Aisin, NPW. Stick to those brands.
And honestly I would buy all new cam sprockets from Subaru. We are starting to see older plastic cam sprockets from the 90's just disintegrate without warning. This results in severe valve train damage.
GD