Hi there, I built a Deans Cossack many years ago, and no, there wasn't very much info for deck beams etc, only some undimensioned sketches in the instruction book. If you approach the job in a logical manner, all will fall into place. As I recall, 1/4 square timbers were run around the inside of the hull, 1 mm down from the edge (the thickness of the deck). On the printed plastic sheets, you will find the decks, , the beams will need to correspond with the openings under the superstructures, and you will also need to put one at the rear of the fore deck, to support it at the fo'csle break. If you work to the decks, you won't go wrong, cut the decks out oversize slightly to start with and sand the edges to fit the hull. You may find the hull sides have bowed inwards slightly, this is normal for a glassfibre molded hull, so be aware of it. As far as the motors go, cut out for the shafts ( the position should show up as fine lines molded on to the underside of the hull) Assemble the drive train, motors couplings and shafts and position in the hull, when all is lined up, you will know theposition of the motor mounts, make sure the shafts are parallel before fixing.
Hope this is of some help.
Nick.