Buddy of mine had a D-800 with the 413 and manual trans and two speed rear axle.
Was an enclosed car carrier he used for years.

My first trip in it was to head to Gainesville, had my car out back. We stopped for dinner the first night and as we walked away I looked back at the rig and noticed an orange glow under the front of the truck and thought it had caught fire. I ran back to the truck yelling and my buddy laughed and said it was just the glow of the exhaust manifolds.

They were bright red. That's why the heat shields are there.

Foot note - we lowered fuel consumption by adding a windage tray, flogging the carb and changing the timing. Managed to get it to - 5-1/2 mpg.