My guess is the log truck has a Spicer 5 speed direct drive.
Is this of any help? http://www.chevyc60.com/the_transmission_page.htm

If not an OD transmission, then high gear will be direct, just like most all non overdrive transmissions.
If you have determined you need an OD transmission then that's what you need, there are no substitutions (other than taller tires and faster rear axle gears).
Also note that not all overdrives were created equal, ratios may vary from about .84 to a fast .61 or so. .8 is common in big truck transmissions, and .73 is common in medium to small transmissions. The .6x ratios are usually the second overdrive gears on some transmissions (double overdrive).

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-