If you insist on building your own arms Funk, there are a few things to keep in mind. You cannot just build longer control arms by adding length to the design of the factory arm. If you do so the truck will have so much negative castor it will be un drivable. You can to move the balljoint out and also re-center it in the control arm. Its really hard to describe but you need to make the suspension function the same as it does now but longer. Since the control arms mounts at the frame are on an angle its not as simple as just adding length to the control arms.
This conversion is not to convert a dually to 3/4 ton but to add length to the control arms to help the geometry of the suspension and also allowing the suspension to be narrowed so turning at a lower height is possible. People keep saying its a conversion to 3/4 ton but really your using a 3/4 or 1 ton single rear wheel truck front hub. Its shorter than a dually hub so you can add length to the control arms without the wheels sticking out.
If you think you can figure out the math involved with building new control arms then go ahead, but I would recommend buying them if your not 100% confident.