Using the overdrive trans isn't necessary unless you plan to pull a trailer and some weight. As mentioned you can use the low range to get a heavy load moving by splitting the main and aux box and stepping up thru each gear. Without weight, there is no point to use the low range. You could use the overdrive as a splitter to reduce the rpm drop between gear changes on the upper end and for more top speed. Driving a 2 stick takes some practice and there are no syncros in the aux box, so you need to match speed and rpm when shifting it. Double clutching will help but isn't like moving the stick from one gear to the next in the main box.

1952 Chevrolet 6400 flat bed