Dude, i cant really help you except for the fact your talking about a steering arm, not an idler arm. Maybe use the ra60 ball joint, steering arm and lower control arm? or maybe the ra60 balljoint will push into the ke20 lower control arm, i have no fuckin idea. maybe someone has done this before. use the search button. ALso make sure the outer tierod bolts to the ra60 steering arm, or you might need to see if the outer tierod from the ra60 can be used as well.
goodluck.