Welcome wc54!
Using my '51 as referrence, those rails in your photo are actually part of the bed. Here is a photo of mine when I refinished my
BEDWOOD They are flipped in orientation from your picture and go where they are in my link above. The third one is at the front of the bed under the front bed panel. You can see the carriage bolts that fastens them to the frame along the top of the frame near the bed sides. In the stock orientation, these bolts should actually go through the bedwood with an off center washer. The previous owner installed them this way and I like that it hides the bolts under the bedwood so I left it like that.
There should be many smaller holes along the solid part of the support that the bolts for your bedstrips will use.
