I can't help with the ID but your pics sure brought back memories. My Dad had two of these commercially built garden tractors. He and I used them in our garden for years when I was a kid. I remember ours being yellow in color not orange but Dad may have painted them at some point. The handle slid the entire motor forward to tighten the drive belt. Kind of a precursor to Gravely tractors. The Briggs NR6 was used on a variety of tractors from 1940-54. Simplicity, Speedex, Bolens, and Farm-ette are a few tractors I recall.