Viewed from behind, the part that attaches to the bulkhead is 14 1/8" by 3 1/4" high. Viewed from the side, the piece makes a "U," with the front of the piece 3" out from the bulkhead, and the side opposite the bulkhead rising 2" up and being 1/2" thick. The part of the U that rests against the bulkhead is 1 1/2" thick, leaving an 1" gap where the table sits.
I just realized I forgot to get the depth of the bottom of the "U." Mine is actually bent, so whatever it is, you're probably better off making it a bit thicker anyway. I'd guess about a half inch.