I've been making some Titan II to double hose conversions the past several months. These are based on the single hose Titan II and the FX reproduction cans available from Rob.
This is nothing new, and others have done these in various ways. The Titan II was made with the same first stage casting as the Trieste double hose reg. They simply blanked off an existing second stage drilling and hard seat. One of mine had a second stage body, seat carrier and soft seat and spring installed to seal the hole. Unfortunately, they didn't install a Trieste body, which would have made things much easier. The other two had a simple plastic plug.
So, one needs a substitute second stage in order to make this into a double hose. To complicate things, the Titan and Trieste are threaded differently than the US Divers bodies. The Voits have 24 tpi threads, and the USD regs have 27 tpi ( an odd choice, IMO). So you can't easily do what might seem at first to be the simplest answer: install an HPR.
The threads are similar but different enough to give pause to the intrepid modder who may consider just running one on in. I actually did this. It worked, and the threads were realigned enough to fit quite nicely. But, the machinist in me rebels at this kind of roughshod running over of things, and things don't really line up right. I have zero misgivings about the threads. They are solid and the realignment took place on the HPR body, not the first stage body. The second stage cannot blow out of the hole or some other type nonsense prediction of doom. But. the HPR was designed for a different regulator and the orientation is wrong for the lever and for the jets. The HPR does work, and its performance is adequate, but not what it could be.
So, I made new second stages and levers that fit the threaded hole, interface with the diaphragm correctly, and have jets aimed the right direction. They are not that difficult to make, and they work very well. In fact, my venturi is too strong without throttling it down with a DSV mouthpiece. One is made of brass, and two others are made of delrin. They work equally well.
IMG_4473 by Vancetp, on Flickr
IMG_4532 by Vancetp, on Flickr
IMG_4531 by Vancetp, on Flickr
While I was at it I made a plug for the J valve hole that accepts an SPG
IMG_4500 by Vancetp, on Flickr