'64,
First you need to identify that you have the original Dana 44 axle. Look at the front diff cover and to the lower right on the housing you will find some casting numbers "44 - 5F". This is for the 1/2T - 6 lug, closed knuckle axle. This casting number is also on the driveshaft side of the housing. You'll probably have to clean the diff housing with a wire brush to read the numbers.
If your truck has 8 lugs and is really a K10 (and not a K20) someone has put 3/4T axles under it.
Is your transfercase in the center of the truck or attached to the tranny? Stock tranny is the SM420, with reverse to the left and down.
Post some pics of the truck, axle, and the "c" knob...
