A 140 rear end might be more problematic and I'm not sure if it's the same track width. An 1800 rear end would be far easier. Keep in mind, however, the 1800 disc braked rear end will have a different bolt pattern (5 on 108 mm ~ 4.25") than your front wheels have (5 on 4.5") so you'll either have to get the front rotors and hubs from the 1800 and put them on your Amazons or make some other accomodations to standardize the bolt patterns.

Hang on a second... According to my interchange manual, not all 122 wagons had Salisbury rear ends. It appears to indicate that some wagons had Dana/Spicer 27s and 30s and the axle shafts and other differential internals are interchangeable with same era 120 sedans, 1800 coupes and 544s with Spicer type axles.

So that means you might be able to find a '66 or earlier 122 wagon with a Dana 27 rear end in it. If so, it would be a direct swap for your wagons and then all you would need to do is find a 10 splined Dana 27 LSD and you have your posi.

Roj

'67 1800S, '69 122s and other 240 sedans.