66 plymouth Valiant Wagon rear section... .

I had similar thoughts. That looks like a '65 or '66 front bumper mounted on the rear ('65 w/amber lenses? Looks like the Aussies used those for blinkers, and the backup lights are up by the taillights). When I had the rear bumper off of my Dart wagon I put a spare '66 Barracuda front bumper up there, and it wasn't a bad fit except for the bumper reliefs in the lower quarters (sorry, didn't think to take pics). The Barracuda (Valiant) bumper has slanted ends, Dart ones are more vertical and I think they'd blend better into those reliefs. Use clear '66 parking light lenses and you'd have built-in back up lights, too. Then it would just be a matter of removing those teardrops from the quarters and welding in some flat tin. Bumper brackets would be up to you, might be able to mod the stock rear brackets, I didn't look into it that far.
I ended up using the stock rear, someone made me an offer I couldn't refuse for the Barracuda bumper.