Here is the chassis from the Bachmann 44 ton with the original silent decoder. Note the arrow in the lower fuel tank indicating the "Forward" end of the chassis. I added an arrow on the bottom of the fuel tank to identify the front when the unit is closed up.

Note the colors of the decoder wiring or reference the schematic, then remove the decoder by unsoldering the wires. Another thing that is recommended is to remove the 2 capacitors (C3, C4) just below the green inductors in the picture. For a schematic of this board, click Here. The front headlight LED will need to removed and will be reattached later.

Here is the body from the 44 ton switcher after the chassis is removed. Remove the hand rails and the cab; it is a snap fit to the body. Next, the top portion of the body needs to be cut away just above the center pedestals as shown here. The depth from the deck to the cut is about 11 mm ( 0.433") or just above the vent slots. This is just below the window line in the body.

The end sills will remain but the sides need to be trimmed to allow the box cab body to fit down over them.

You will also have to trim the ends of the box cab body to clear the end sills.

Additional info can be found in the similar conversion of the Box Cab Diesel on this site.

These views show the speaker enclosure sitting on a shelf from a piece of styrene and the Digitrax SDXN136PS sound decoder connected to the motherboard. The included capacitor should be insulated as the case is connected to the negative power. I wrapped it with Kapton tape.

Note how the forward light has been replaced with an LED bulb in the headlight casting and wired with a connector for convenience.