A little early !
there is nothing to say that you could not score on the Moy in March, but it is a little early.
Your chances will improve enormously if you can leave it until April, with the main run of springers arriving then, and more suitable conditions.
Water levels vary from year to year but April usually provides good sport on the fly.
Salmon are caught from early in the season on the Moy (opens 1st Feb), but most early fish are taken on spinner or worm.
Please let me know if you need any contacts over there, as I know it well.
Best of luck,
Luck, is when preparation meets opportunity.