Do I need trailing arms on my custom IRS chassis?

[dave96dcm]

I'm under the understanding that any "arm" that is parallel to the axle and connects the spindle to the frame above the axle centerline is a upper control arm, if it is below the axle centerline it's a lower control arm, if it is in front of or behind the axle centerline and is for controlling toe it is a tie rod "or toe link". If it is perpendicular to the axle centerline it is a trailing arm or "swing arm". That could also be upper or lower. Shape/size/number of attachment points don't matter, that's what it would be called. Or at least from my experience.