Friends recently put ducks in the freezer. Plucking a duck is not the same as plucking a meat bird, especially those meat bird desgined to be easy to pluck.

TO save himself the agony of plucking, they only harvested the breast of the bird, skinless. There is very little else on the average duck carcass to make it worth the effort of plucking.

I know that Muscovies are larger and may indeed have drumsticks worth eating. But if not, you might consider simply taking the breast and not plucking at all.

As for cooling, I have nothing else to suggest other than our tried and true cold water chilling, with fresh, cold water added often to keep the temp down. You want to put COLD objects into your freezer!