looking at this again with a phot of Simms on his quad the maindifferences appear to be the gun mount and amo box arrangement and the engine. Everything else looks much the same. Could there have been a Simms Mk II ?
According to the blog the picture is from, this is in the "RSL Military Museum" in Alice Springs, Australia. Seems that the museum also has a website: http://www.alicespringsrsl.com.au/museum.shtml
According to the site:
The centre piece of the display is the motorised and/or pedal power "Quadricycle Gun Carriage". It is the only replica known to exist. The original machine was first built in 1899 as a passenger carrying vehicle by the Great Horseless Carriage Company in London. Shortly after, a Mr. F.R. Simms modified the chassis, and installed the first fully automatic gas operated machine gun to create the "Gun Carriage". As a fighting machine however, the Quadricycle was not a stunning success. It does, nevertheless, stand as a testimonial to man's ingenuity.
The replica was constructed in 1990 from photgraphs of the original Quadricycle by Alice Springs resident, the late Mr. Don Bennett.