To remove the coal load, slip a small jewelers screwdriver between it and the long side of the car body to make it pop out.
Adding weight to this car is trivial considering I also plan to put a load in it. The model originally weighs 0.5oz (14g). It needs to weigh about 0.95oz to comply with the NMRA recommended practices. I use lead shot to provide the weight. They are superglued to the bottom of the car after I evenly distributed them.
This is the unmodified Bowser car. It is a nice basic model. It is very light, has truck-mounted Rapido couplers, and an unrealistic-looking coal load.
The two lines in the next photo point to the two truck pins that can be popped out to remove the trucks.
When I did that, the center part (the metal structure that provides the model's weight) came loose as well.
To start the coupler conversion, I first needed to check the body's height as compared to the Micro-Trains coupler height gauge. This photo shows a close-up of the check. It is very close.
Before being able to install the new couplers, I needed to remove the old couplers from trucks first. Using a small jewelers screwdriver, the lid from the old coupler can be removed. You can put the lid back on after you have removed the Rapido coupler, if so desired. When the coupler gone, the body-mounted Z-scale coupler clears the trucks.
A part of this hopper car is the metal sub-structure of the car. It adds the (small) weight of the car and holds the trucks. There are two small holes that are a perfect fit for Micro-Trains N-scale couplers' screw. The screw that comes with the Z-scale coupler is thinner and shorter, so it doesn't fit the hole. I decided to use the N-scale couplers' screws to mount my Z-scale couplers. (I never took a photo of the Z-scale coupler installed).
Since the car has a sloping interior, it is relatively easy to create a fake bottom from 0.040" styrene. The original load was used to determine the size of the piece of styrene.
The photo below shows the piece of styrene installed in the car. I glued it in place with Testors Plastic Cement, since I wanted a permanent load.
Should the edges be visible, I painted them black (paint is still drying in this photo).
I used Woodland Scenics' "Mine Run Coal" (part #B92) as the coal for this load. It provides a rough coal load, fresh from the mine. The idea for creating this load came from the June 1990 Model Railroader article titled "Economical Coal Loads" by David A. Bontrager. The article covers HO-scale hoppers, but the same idea applies here.
I used Matte Medium evenly mixed with water for the glue. I sprayed household rubbing alcohol after I placed drops of glue over the styrene sheet. This caused the glue to saturate the whole area.
I kept adding layers of coal and glue, forming a raised ridge down the center of the car. I determined the load height based on prototype photos of these PRR hoppers.
Here's the final result. It looks a lot better than Bowser's original load. You can vary the look of the load to your heart's content to get that custom-loaded look.