Cannot see a Vic marriage but unless he changed his name it definately appears to be MCGUIGAN..
Brothers war records from NAA
MCGUIGAN JOHN ROBINSON : Service Number - 142312 : Date of birth - 01 Jul 1911 : Place of birth - WILLIAMSTOWN VIC : Place of enlistment - MELBOURNE : Next of Kin - MCGUIGAN RUBY
Tere is a Patrick James MCGUIGAN in NSW (only Patrick James MCGUIGAN I can see so far on Elect Rolls) he dies in 1941 but father listed as James.
26722/1941 MCGUIGAN PATRICK JAMES JAMES MARGARET RANDWICK