'Shorter' is usually a matter of only 1-2 mm, i.e. not much. If you are bothered by the presence of the adaptor (many are), a better option, less expensive than a new 1st stage, is to simply get a yoke bolt and A clamp for your current first stage, and convert as necessary. I dive a DIN Zeagle 50D. When I go to the Caribbean, I convert it to yoke for the trip. Takes 30-60 s.At this stage getting another 1st stage is pretty much out of the question. So what are the shorter ones? Less expensive ones?