You can have new glass cut to make the windows one piece (No vent window). You cannot install 48-50 window glass in 51-54 doors because the 48-50 window glass is thicker with the metal suround. The interior window garnish molding is thinner on the 48-50 doors. To put one piece glass in the 51-54 doors you'll need to cut out the brace where the vent window mounts and make a new window channel for the glass to ride in. If you have any fabrication skills, it's a fairly easy conversion.