Ford did not use a Panhard Bar on the front of any Early V8. You are using the wrong terminology, the bar used on the front suspension is a stabilizer bar used to control/minimize body roll on turns. Ford started to use this type of bar on the '40 Delux cars, and all '41 and later. If your '39 Merc has one it could be after-market or a special application for export only.
A Panhard/Sway/Tracking Bar is a devise that is securely attached to the frame and suspension, to maintain alignment of the components. Generally on coil spring suspensions. A bar that has movable links is not a sway bar, however, many people commonly refer to this type of bar as a sway bar.
C & G Early Ford Parts (760-740-2400) (
www.cgfordparts.com) shows the parts for the '40-41 Stabilizer bars on page 48, section 6 and the complete assembly on page 49, section 6.
I have a stabilizer bar on the front of my '36, 41 front axle w/2" drop and a sway bar on the rear, '47-48 Columbia.