Got Shell 93 Octane and now barely idles 1973 Dart 340

340s are supposed to idle rough. That's why we found them attractive back in the day; Factory race motors.
But I get the sense that your 340 is rougher than most.
Here's the deal; A stock 340 came with 5 Measely degrees, and stick cars idled just fine at 650 rpm with those 625AFBs.(I don't recall A/Ts, cuz I never had one). Power-timing was 36*.
So if your T-port sync is right, your Carter should also idle just fine at 650/700.
With the correct T-Port sync ; if yours does not, then it may have a mechanical issue.
So Having proved the T-port sync correct,and it is still rough, then you will have to do a compression test.And maybe a LD test, and maybe you will have to check the cam lobes or the cam-timing.
But before I would do that, I would pull the plugs for inspection. And I would check out the wires. These are easy to prove OK or not, and cheap to replace, if bad.By this time I'm assuming that the vacuum leaks are gone. I'm also assuming that your funky new carb-adapter has not introduced it's own odd running characteristics.I'm also gonna assume those EGR tubes in the bottom of your intake have been mechanically plugged, and that the AFB idle circuits are working. So that's a lot of assuming going on.But after all, we are on page 5 already.
But if the T-port sync has never been set, then you can spend hundreds of dollars and still have a crappy-running engine.Since I have not yet seen a report that yours is ok, Im assuming you havent checked it; and we are half way through page 5.And I'd rather not hear anymore about where your timing might be. You need to know where it is--exactly where it is ..This is most important as the rpm climbs,and as the loading increases.