Look in the inlet side, where the air filter clamps on.  On the bottom, you will find a passage that intersects with the needle jet.  That's it.  Some were tapped and had changeable jets.  Alot of them are open with no brass, in the realm of 1.5 to 2.5 mm I believe.  Should be able to tap it and put a 0.5mm air bleed into it.  As others are saying, it may work with the other jetting.  It's probably worth trying before you have to go all the way with it.  Start rich main jet, pull the needle up 1 or 2 clips.  See how your part throttle response is, and note how clean it is. Could be rich and burbly, or it could be lean and surge.  Only 1 way to find out.  Want a slight burble, but it should clean up with load.  Never want surging or racing, any part of the throttle range.

The air jet only affects the main circuit significantly at near full to full throttle and higher rpm... 

On the "primary" type needle jet...  the type with the little shroud that sticks into the airflow that both DT carbs had...  a bigger air jet makes the mixture a little richer at full throttle and high rpm.

If I remember correctly the DT2 carb has a bigger air jet drilled so that = richer which = safe.  Air jet doesn't have that much effect...  more of a "fine tuning".

P.S.  You can't clean the carb completely without removing the needle jet.  A lot of crud sometimes hides there.  Presses out from bottom to top.  A small hardwood dowel often works great as punch...  Rick C uses a chopstick..  make sure not to loosen or damage the brass locating pin with whatever tool you use to tap the jet out. 

Markt, that is good to know on the air jet function. I just see a number, and want it to match. Initial thought thinks leaner with more air, but understandable that it would help draw more fuel.
Are you open to a discussion about the function of "bleed" style needle jets? Not here probably.

Many thanks,

I've already ordered the correct (by part number) needle jet and jet needle (nah, that's not confusing...). I'll run a 165 or 170 main, whichever I can find, since the consensus seems to be they'll work fine. All else looks good and I essentially have a 214-E4... I report back on how the machine fires up once I get everything all the pieces.

Very much appreciate the great help I've received on this forum. I can't post pictures here but will provide a link of the final result.