For a long time, there were no conversion kits available for 3/4 ton trucks.. There just was not enough demand for them, since the original equipment drum brakes were very adequate for stopping them, given that most stovebolters don't use their trucks to haul the maximum gross weight loads the trucks were designed to carry. The vendor has explained what's necessary to make his kit work with your truck. There are several other modifications necessary for a disc brake conversion to function properly- - - -changing to a power boosted master cylinder the right size, running new fluid lines, and possibly installing a proportioning valve to prevent rear wheel lockup when running without a load in the bed. If enlarging a couple of holes in the spindles and steering arms is a challenge, maybe you need a little help from someone with a bit more experience at making modifications to a system where a mistake can be deadly dangerous. Disc brake conversions might be the current fad, but a good rebuild of the original system is a lot simpler, less expensive, and potentially a much safer choice.
Jerry
