You said it is a 84 3/4 ton, it should have come with the 14 bolt already installed. So I am assuming it is a newer version he swapped in, you could always look for 1 in like a junkyard and pull the parts off you need to swap the components for the e-brake if that is even possible.
I assume if you can buy them that it is possible, but I personally have never done that so I am guessing.