If the rack is NOT mounted to a frame rail, it must be mounted to the front crossmember
Not a good place to mount it ... because of caster changes when the suspension moves up/down. OR ...
You can mount the rack to the axle
to eliminate the caster changes ... but then you need a sliding u joint to hook the rack to the steering column. PLUS the added weight on the axle adds to the unsprung weight. ADD ... it is UGLY.
DEUCE ... Moderator