A body parts manual for the Ford of those years and one for the Mercury cars of those years will answer part number differences but may not answer anything else. If parts are available for the opening quarter vent type then I would just repair what it has. Changing it may not be all that practical.
In the mid century Mercs of 1949 through 51 that I'm more familiar with, offered two and then three different 6 passenger coupe models. The standard budget model has fixed windows but the upper scale model and the later Monterey model had the flip out vent windows. The flip out type vent windows had their own frame that fit with the inside garnish molding. The standard just had a plain garnish molding with a rubber seal to hold the window glass. The seal has a groove for the stainless molding that is fitted to the outside. These type seals hold the glass to the pinch weld just like the rear window. Just try to find a specific seal for a fixed quarter glass. They don't make them for the 42 thru 48 fixed glass models. A person has to purchase bulk seal material and cut them to proper length and the join them together on the bottom for a clean looking and leak free installation.