Why would Antimony (Sb) and Aluminum (Al) be confused?
Yes, they are chemically fairly similar in their natural state, as well as tin; all very light coloured metals, less dense than iron. China is still (as of 2017) the world's largest producer of antimony, accounting for over 75% of global annual production. 

There is another dimension to this, which is that antimony has been known since antiquity, way before aluminium, in the West and in the East. However, in ancient China it was generally considered to be the same as tin. One of the largest antimony mines is Xikuangshan (錫礦山, lit. Tin Mine Mountain), in Lengshuijiang (冷水江), central Hunan, and was thought to have been discovered in 1521. 

Antimony was given its modern Chinese name in the 1870s. Straying into speculation, I think that it would have been enough time for 銻 to have diffused into common use (and move away from 錫) in the southern topolects, maybe under the influence of this mine in Hunan. So I'd expect 銻 or something like it to be common words in Xiang, Sichuanese, Gan, maybe Hakka and Cantonese. Again, just a guess, but something to check! 

It would be very difficult to trace the production and nomenclature of aluminium goods in the post-war of modern Chinese history, but not impossible if you were in the local community. You would have to ask the 单位 which was responsible for either manufacture or transport of such goods, or some HK vendors from that time.