I thought at first Cobra 29 was referring to a TOP cover for the pedal box opening. I know that one came with my car, but somehow, I misplaced it.
I finally got around to fabricating a replacement. I took a sheet of aluminum, about 7" x 11", and cut slots in it for the pedal arms to move in. I then riveted on small strips (about 1/2" wide) of aluminum on either side that secure a strip of thin rubber (about 1.25" wide) that overlaps in the center of the opening. This allows the pedals to move, but seals out any heat (and dirt, dust, etc.) coming from below.
If you really don't have the lower box, I'd start there, but then I would add a top cover, too.
regards,
cobrajeff