The runnin' board doesnt bolt up at the rear of the door. It continues to the rear fender well and is supported by a brace on the frame. I've had to repair several of these that had the "boxes" rusted out. If its a coupe, pull out the inside trim panel and look down, theres the rest of your runnin' board.
Thats why I asked if it was a 4 door, but they have a rear quarter between the rear door edge and the fender too. I can take a pic of the running board mounts on my 47 for you tomorrow. The running boards are gone, but the brackets are still there right now.
It is a convertible. I have replaced the box and have the bracket. Only on most cars I have pictures of (have running board installed) there is a bolt that is between the box bolts and the support bracket (links to the top brace). I was hoping someone had a shot of the rear without the running board installed.
Sorry...clarification. A pic from below the car without the runningboard installed. Thanks for your help