I have always wanted to build a logging speeder and built a static model of one several years ago. In my search for a mechanism, I found a HO scale four wheel Athearn EMD Model 40 Diesel locomotive with the dimensions I was looking for.
Once I removed the Diesel’s shell, I could see I needed a new floor with a narrower opening for the Diesel’s mechanism. I made a new floor from sheet and strip styrene to fit the mechanism.

Next, I built the speeder’s shell from V Groove Styrene siding. It is 17 scale feet long, 7 feet wide and 63/4 feet high. I added Grandt Line caboose windows and doors for the crew. I even added the heads of sewing pins for the doorknobs. The roof is sheet styrene covered with masking tape to represent tar paper. Other details include a fabricated headlight bracket and headlight with an MV Amber lens from my junk box, an HO scale single chime horn, and a Grandt Line Reo Radiator, along with the appropriate handrails to finish the body.

I glued two benches for the crew and a seat for the driver in the interior, and covered the Athearn mechanism with electrical tape painted grimy black. Then I added wood end beams and footboards with Rio Grande Models #3535 sled plates to create the look of link & pin couplers. I added smaller footboards with brass flat bar stock for the supports under the side doors.
I completed my speeder with a crew and some weathering. All in all, it was a relatively simple project at a reasonable cost, you should give one a try!
