I have seen approximately 15 1948/9 Suburbans and have never seen one that came originally with barn doors. There are impressions for the barn door hinges, the rubber covers over the hinge holes but I don't believe that there are any holes for the checks.
Clamshell doors need trunions, cables, cable retractors, hinge mounts under the rear door sill, holes for the lower tailgate hinges in the body fill strip under the rear doors, tail gate catches (both sides), rod bracket for tail light, upper tailgate supports, upper tailgate hinge mounts in header.
If you have a barn door on an early suburban, then there may be modifications to all of these locations. Most likely the retractors will still be in their location, there would be holes or metal patches in the header to close off the holes left behind from removing the upper gate hinges, there could be patches covering the hole for the trunions or a flat piece of sheet metal in place of the original impression and if you look under the rear sill you will see remnants of the tail gate hinge mounts.
The door check that Tim shows as the one for a suburban is correct. They use that check so that it will work with the cardboard headliner that is not in the panel.
Tim also shows one of the panel checks and I agree that there were two.
