For HO and larger scales, small LEDs can be mounted directly on the caboose ends. If you’re in N or Z scale, you may wish to use one of Heinz’s alternate techniques — “…on some modern cabooses, use a single LED& fiber optic to get the marker lights to the roof ends; drill 2 small holes (tight fit) in to the LED and use heat shrink tubing to darken the LED and hold the fiber optic in place; route them through the back wall and glue the fiber optic under the roof corners )3/32″ past the ends); once the glue sets (with a soldering iron, close by) melt the fiber optic to form a mushroom.”
On work & transfer cabeese, you may prefer to disguise the caps; he mounts them outside the ‘boose and paints them like tanks for water, oil, fuel or weed spray. 500uf caps can be used if space is greatly limited; likewise, caps with a 16 volt rating may be used if you’re absolutely sure that the DC voltage on your tracks will never exceed 14 volts — in any case, you may confidently substitue 25 volt caps in lieu of the 35V ones shown and save a bit of space. Shown below is Heinz’s original drawing for this circuit; he does good work!