Early A Rear Sway Bar Install Pictures? Mounts to Axle

Most aftermarket ones I have seen mount to the axle with U-bolts. The arms point forward and mount to the frame rails, with short end links.

While mounting to the body is superior from the standpoint of unsprung weight, the physics are the same either way. Mainly, design & packaging is much easier, since the axle shape is always the same -- only the length and spread of the arms have to be changed for different applications. A body-mounted bar would need to be custom-shaped for every different application.

At least one vendor makes a body-mounted rear bar for later A-bodies (might be Hellwig). I don't know if one is available for early cars.