I've only ever heard of TC arms breaking in extreme jumping conditions (100mph nose dive sort of things, coincidently also wrecking the truck.)
So, I would advise you to drill out the stock relay rod, not bother with the idler arm, since its extremely unlikely that you will break it. I won't say impossible, but thats the way I'm leaning.
I would carry an inner and outter tie rod end, and one or two adjuster sleeves, as they are the weakest part.
Baby Beast 2- 1999 4Runner SR5
Baby Beast -1987 4Runner SR5-Gone, but not forgotten