A 2" coil spacer will add 3" of lift. The Duff lift brackets are 3". With stock steering and the TTB, it's necessary for handling to keep the axle beams as parallel to the ground as possible. The radius arms aren't the issue--front end jacking with uncontrollable steering are the issue. My truck has an old 3" Duff lift with saggy Jeep XJ springs. It's probably only 2" of lift, but it handles great. Being able to drive it must take precidence over height. Plus, you don't want to wear out $800 worth of tires. I've had the same tires since 2001, except I had to replace 2 out of 5 due to torn sidewalls. They have not worn from being stupidly aligned.
I have played with spacers before and you get a lot more than you think you will. This TTB just doesn't work with spacers. If you need to lift it a bit for alignment purposes--side to side leveling, you need to use big steel washers under the spring pads.
I'll tell you right now--few alignment shops know how to align TIB/TTB. If they don't hold the truck up under the tires, it will be WAY WRONG when they set it back on the ground. I did that years ago and never went back. You can't just add spacers under the springs because the alignment will be way off. You have to know what you are doing to get it back, and it's unlikely you have the camber bushings in there to align even a mild increase in height.
This suspension is retarded in many ways, and excellent in many others. Whatever you do, you will need to align it. I wouldn't muck with it unless you are serious about learning how to do that. It's simple, but tedious.