I have an antique headboard and footboard along with the one piece iron frame that attaches to it. Problem is that when you attach the frame to the head and footboards, the "L" shape is upside down so there's no way to use slats or to secure the mattress in the bed. I can't turn the frame upside down because the holes in the frame and the bed wouldn't align properly (there's also a small nodule on the frame that fits into the head and footboards). Any help/suggestions/advice will be greatly appreciated. I used this bed in a former home but that was over 30 years ago and I just can't remember how it was set up!
It sounds like you have the rails swapped. Right on left and upside down. Try moving them to the opposite side and turned top to bottom I think you will find they fit that way and hold the slats in place.