When you put in a DST, straight up from the adjusting screw is about where you want the triggers to trip the sear. This position will tell you if you have enough room in your trigger guard bow to accommodate the DST assembly.
Your trigger guard is located to accommodate the single trigger and may not give you room for a DS. It looks like it is placed a little too far forward.
I would bet your trigger is pinned, you can make a new one easily or solder a piece on the top of the trigger bar to change the angle. I have soldered on extra metal a couple of times, it came out well.
Cold forging a trigger is kind'a fun, I have made all my single triggers so far.
Here are a couple of ones I just started and one I finished.
Finished;