Swapping the entire front suspension from a '71 half ton is probably the cheapest way to put disk brakes on your truck, provided you can find the suspension real cheap. I have one from a '72 3/4-ton I got for picking it up, they can be found. '71 because it is the only year with both disk brakes and six lugs.
Unless you're driving this thing like it’s a race car or carrying far too heavy a load the stock brakes should be adequate under most circumstances. You might want to find a manual and make sure the brakes are properly adjusted.
