Hi JB, the last picture shows it well ... everyone says replace the Atlas couplers with Kadees, so Atlas replaced their originals with Kadee 8xx lookalikes in response. Then Kadee brought out the 7xx variants to stop too much praise(?) for the P48-loving competition.
The original Atlas China couplers (look very much like the original Roco-tooled version) have a long fixed arm on the knuckle and when you try to couple them to a Kadee the clearance is a bit too tight. Take your end cutters and snip 1/16" or 1.6mm (I keep up with changes) off the fixed bit of the old Atlas knuckle and file it smooth, it will couple. I also replace the Atlas steel(?!) spring with a spare Kadee p/b.
I've posted this ramble on a few sites, so apologies if I have done it here before. If it doesn't improve matters to your satisfaction, apart from fitting Kadees, I wonder if you can get new version Atlas couplers. They should be drop-in replacements using the current box I think.
And yes, P48 wheels... this week, just had a pleasant week with grandkids, but back to reality.
Jason