It's that add-on piece that you put the rubber under,between it and the crossmember.It's held on by the two bolts on the ends of the clamshells.If it doesn't have the clearance between it and the crossmember for the rubber to fit without lifting the rear of the trans,then something else is bent somewhere.That is not a Ford part,and can't be used with even a slightly bent frame.There is a theoretical reason for it being there,but with the roads and use the A's get now,I've never seen a problem without it.My uncle parked his 30 in 1954,it had floaters but that part was under the seat.I've driven the truck 56000 miles since I got it,still without it,with no problems.I have gone through a couple of sets of rubbers though.