Firstly - a massive 'thank you' to arockStone for the wonderful Diesel Loco model! My small modifications would never have existed without such an excellent starting point.

My small garden railway is 32mm gauge, and to emphasize the 'narrow gauge' character of the loco I decided to modify the chassis so I could move the frames closer to the wheels. This meant modifying part 1 from the frame_1b.stl file to reduce the width. As I print in ABS, there's also a potential warping issue with the raised portions of this part so I split the long flanges into separate parts (base2.stl, 2 copies needed) which can be glued to base1.stl.

Having started making changes, I then got a bit carried away...
Frames (frame_V4.stl, 2 copies)

• the spring detail on the frames got lost during slicing, so I modified the suspension details to add hangers and make the spring leaves visible
• removed the lengthwise flange
• reprofiled the frames and added cutouts to make dummy brake gear (brakes3.stl) visible behind them

Buffer beams (buffer.stl, 2 copies)

• made rectangular and some bolts added
• increased the size of the coupler slots
• reduced the hole size for the coupler pin (I used hard brass wire pins)

Hood

• I wanted to fit R/C to the loco, so I couldn't afford to lose the space taken up by the dummy panels 22 and 23 in hood_3b.stl. Instead I made a cut down version of the engine (engine2.stl). This has the transmission removed and can be fitted next to the electric motor
• there's space in the headlamp to fit a surface-mount white LED and resistor so the lamp can illuminate. lamp.stl is modified to have a tube through which fine wires can be passed (just drill a hole in the hood top to pass the wires through into the engine bay). The lamp bezel and lens are unchanged
• I made a more complicated silencer/exhaust pipe (exhaust2.stl) and modified the hood top (hood_tp.stl) to support it
• added a horn (horn.stl) to increase the 'clutter'. This and the exhaust are printed in two halves and glued together

I wanted somewhere to hide the batteries, so made a console to fit in the cab. There's room to fit a double AA battery holder inside. The console consists of

• a base (batbase2.stl) which provides space for a switch to be fitted underneath while the battery holder sits on top
• a front panel (panel.stl) to form the battery box
• the console top (console.stl) with a couple of dials, switches and a throttle lever. This just pushes into place to cover the batteries

And for a few final details

• some steps (step.stl, 4 copies)
• a tank (tank.stl - glue the two halves together). The 'flats' are for fitting under the footplate and against the frame.
• finally, a nameplate (MrGrumpy.stl). Unfortunately the choice of name seems to have been rather prescient - I'm having terrible trouble getting the R/C gear to work!

Note - I have only provided STL files for my modifications, so you will need to download the original model by arockStone (https://www.thingiverse.com/thing:2109286) for the rest of the parts.

Last of all - thanks again for the original model without which none of this would have existed.