In part it depends on what look you're going for, wheel offsets you like, and so on. The "ideal" is something right near 56" mounting flange to mounting flange. In an 8" that would be Maverick/Comet, in a 9" you'd be looking at '57-9 Ford station wagon. The first gen Bronco was something around 58", whick could work but you'd have to do a wheel with more positive offset. Given the cost of original wagon rears, and they typically need to be completely reconditioned (unless you get unusually lucky) it's a wash in the real cost view to start with a new Currie or similar and get exactly what you want/need. One slight advantage to the Bronco, if you're doing a period/traditional car, they have the 5 1/2" bolt circle, so that could swing the value equation a bit if you can live with the width.