Just out of curiosity, I tried some research about Denbys. All I found was that there was a William Henry Denby of Evelyn Gardens, Belfast, who was a master motor carriage builder (sounds promising....) but he was aged 46 in the census of 1911. Maybe his family continued the business.
The G.Hurst mentioned may have something to do with the present Charles Hurst group, which are probably the largest car dealers in the Province.