I too have an interest in Alexander & Co. in Glasgow. My 1950 Comet was registered new from there. I think it was called J R Alexander & Co 272 Great Western Road, Glasgow. -It went out of business over 2O years ago. My bike was registered as BSN 580 around Jan 1951.
From around 1956 to 1969, Matthew Hood (69 South Scott Street, Baillieston, Glasgow) owned motorbikes. One of them was BSN 580-a black Vincent Comet 500cc (sometime it also had a sidecar). Amongst other uses, Matthew went on fishing trips with his brother John on the bike in the late 60's prior to emigrating with his wife Nancy (and children -Linda, Lorraine & Jillian. Whilst he lived at Baillieston for much of the time from 1956, by 1968 he was working at Honeywell and lived at Blackridge near Bathgate. In 1969 he emigrated to the USA with his wife Nancy and the family. He sold the Vincent Comet to his brother John before emigrating and they dissembled it and stored it away pending a rebuild.
Matthew and Nancy split up in the USA and he died in 1970. John Hood (the brother) died in 2007.
Any info on the ledgers from Alexanders or pictures of the bike would be gratefully received.