I do know his address which was 118 East Street Walworth Surrey.
His son James Gillegin was a member of the London philharmonic orchestra.
Another son William junior was apparently a professional piano player and was definitley a piano teacher.
His daughter Amelia Gillegin (married name Biggs) was a trader of pianos.
There is a strong musical link,and this may indicate that he had his own business but that is only speculation and not fact.
I thank for you interest and any information you have. I was not aware of the website you mention and will look it up after this message.
Best wishes Tony
There was a piano factory in Peckham Road, Camberwell, close by to Walworth. I have often wondered if he worked there. The geography makes sense, and people didn't necessarily work far from home in those days.
Source: The Times 31 December 1883 via Newspapers.com
Apparently, the son, William Gilligan at one time worked as a pianist on Atlantic liners entertaining passengers during the crossings to New York.
He is listed as arriving at Liverpool, England, on a ship named City of New York, on 26 Apr 1892 so he definitely made at least one journey to the States and back.