I don’t suppose your truck is still together? If so, simply take it down to an alignment shop and have them give you a readout. Don’t have them adjust anything, just a quick readout.
Find out where your caster is now, and see if there’s any such thing as too much caster, by simply adding an additional 4° from the T-Rex arms.
If you have, for example, only 2° of positive caster, then adding four more is going to be perfect. Not too much at all. Unless…
Are you going to continue running manual steering, or do you have power steering?
It’s hard to make blanket statements, such as this won’t work. Too many variations and variables on Broncos to do that anymore. Find out what you have, then find out if what you want will work.
If your truck is all apart already, you can’t check. The best solution for that then would be to put it all back together with the normal stuff (meaning stock radius arms), then get it measured.
Then you can make an informed decision as to whether or not to proceed with installing the different radius arms.