Looks like a tight fit. Perhaps a Micro-nami or maybe an Econami? Is front light a bulb? (How replace) Did you install a backup light? I plan on using a cell phone speaker in the cab roof - paint it flat black
No answer yet so try the below.
I do know the Econami is a little smaller than the 750 and not heat sensitive like the 750 is.
The decoder measurements are at the SoundTraxx site. Get your dial caliper out and check the inside of the loco.
Use your ohm meter and check the headlight leads. You should see a few ohms resistance if a light bulb and max resistance if an LED.
Number thirty wire would work and I have used magnet wire from an old relay coil. With a 1k, ¼ watt resistor, about 9 ma current for an LED.
Search the internet for the loco of your choice of railroad and see what the road used for a rear light.
Search Walthers for a rear light in Advanced HO Super details search.
I did that some years ago for a different 0-6-0T loco.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Another suggestion is to Google Rivarossi S100 0-6-0T. I just did. There is quite a lot there including clicking on Images.
Just found this link in search and included installation.
http://www.tcsdcc.com/Customer_Content/Installation_Pictures/HO_Scale/Rivarossi/0-6-0_SaddleTank/rivarossi_0_6_0_saddle_tank.htm