Another update! So after putting the decouplers in place ... Then moving them after some operation testing.  Ive got them in the final position and began running tests. I found the third car would pull itself over the decoupler.  So I added a half bushing and problem solved! And as a bonus the layout with no cars.  I set the roof of the switch house in place to give an idea of layout for me.  The single spur track will store the two spare cars when not active in the puzzle. Still need to build the buffer stops and finish the air operated switches (planed to leave the storage spur manually thrown). . . And once the rest of the parts on a slow boat arrive I can route hoses and finish the cars up.