Nick,
The only time you would have seen trucks like this in Alaska is back in the 1970s when they were building the Alaskan Pipeline. Hill & Hill was one of the contractors that hauled the Vertical Support Members up the Dalton to the Pipeline.
Here is a photo of the steering box location of the AMT Mack Cruiseliner that I built back in 2011. It's not the best shot, but I hope it helps. You can also kind of see it in the shot with the engine.
Looks like a pretty good build.
This might help with your Cummins engine: https://public.fotki.com/modeltrucks25thscale/model_magazine_articles/car_modeller/cm05_jan_1991_cummi/