Yes it is the eccentrics, and yes the little tabs are there. When I try to readjust I make sure the tabs are in place before tightening down the screw. However, if that is not done correctly the rod(s) will bind.
By the way, I mis spoke on the engine, it is lettered for the DM&N but MTH 0-6-0s I am sure were lettered for different roads, sorry for my mis thinking.