Found this idea on the net but was written up in Kalmbach's "Model Railroad Planning 2018". The issue featured Doug Tagsold's Colorado & Southern. The premise is using HO gauge equipment to represent 1/72 scale narrow gauge.

I have a Bachmann sound value gp7 that i run on a dc power pack. It runs and sounds good but going up hill pulling a 8 car train i need to have it on full throttle and the engine crawls up the grade. it sounds realistic and when the grade levels off ican throttle down. When the throttle is on full the headlight is very bright am I going damage the engine?

I visited Paul Krentz yesterday and it was a revelatory experience (I'll try to keep the superlatives to a minimum but it will be difficult).

I'm going to try my first attempt at 3D printing using Shapeways... to prove to myself that I can do something like as much as anything else.  I'm going to try a gondola extension in HO scale as shown in the attached photo, to mate to a Speedwitch Media DT&I 40' gondola kit (#P119) which is a match for the underlying gondola.  The fairly simple geometry and welded construction of the extension seems like it would be a good candidate for my first attempt at a 3D model.