Chas,
I recommend that you take the four screws holding the body shell out of the car. The body should come up off the chassis. The bottom brace will have to be put back in place at the very outer edges at the bottom of the door opening after the doors are re-installed into the upper brace. A very little glue should hold the brace at the outer edges. AVOID letting glue run on the door track/brace. You could permanently stick the doors in the wrong position.
Do a dry run without glue, to see that everything is fitting together. Only the outside corners of the track get tacked in place with glue. The silver brace should NOT be glued to the car floor, only the outer corners of the door track get glue.
Sincerely, John Rowlen