The Contender and Encore have different diameter barrels. The Encore has a deeper, wider contour under the scope base than the Contender. The screw holes will line up, but the base for the Encore will not make good contact with the surface of the barrel of a Contender. I have not tried it, but I suspect that the base for the Contender is shallow enough that the screws won't reach the screwholes on the Encore barrel.
You could probably use an Encore base on a Contender in a pinch with very low recoiling calibers.