Thanks for that great information.
I am going to drill the rivet out and remove the flat spring from the underside.
Do you think it would be wise for me to re-install the flat spring, on the top of the draw bar, pushing against the upper tail end of the engine, so that the spring is pushing the truck down? Do most locomotives have a spring pushing the rear truck down? Have just a single axle and two wheels, the truck seems awfully light and fluttery.