I believe you mean Panhard bar, not trailing arm. The trailing arms run from the trailing arm cross member, laterally, to below the rear axle. The Panhard bar runs from the rear axle to the upper portion of the driver side frame rail. Jack the truck up at each axle tube & put on blocks or jack stands. This will keep the stored energy of the coil springs & shocks in the suspension. The Panhard bar it to assist in controlling lateral movement of the axle. I don't think the Panhard bar on a '66 Chevy C10 had a bend in it, so it may need to be straightened, which can be done by applying heat and bending back into shape.
