Is this a DS I or a DS II?
It sounds like you have an older DS I without a "kicker-pit", that was a feature that most of the DS Is had to allow clamping the outboard directly to the transom. It kind-of looked like a small cooler set into the aft deck (see pics below). The older boats (like 1958-60?) didn't have the kicker-pit and now that I think of it..... had the area under the aft deck closed off to form a flotation air-tank. Hmm! I guess you may need to cut an access hatch into that bulkhead at the aft end of the cockpit to mount a small fixed-height bracket (I wouldn't use one of the lifting brackets, too much $$, weight ,and height for our low-freeboard boats.)
I was lucky, I have a newer DS II and can just clamp the outboard right onto the transom with plenty of room to clear the rudder.