These two men, one from Aird, the other from Portvoller, are (to the best of my knowledge) not remembered on the local Roll of Honour or on the memorials at Garrabost or Stornoway. I happened across Murdo Mackenzie through a search for the age at death for Norman; the two are mentioned on the same "service return" from the General Registry Office of Scotland.
Norman's age at death is listed as Unknown on the CWGC website, but the GROS file shows it to be 38.
Seaman MURDO MACKENZIE
Last address in Lewis: Aird
Son of Donald and Catherine Mackenzie, of Stornoway, Isle of Lewis.
Service: Royal Naval Reserve (Patrol Service), HMS Greenfly
Service number: LT/X8100C
Date of death: 2 November 1939 at the age of 28
Lost through drowning after a fall
Interred: Tynemouth (Preston) Cemetery, Sec. F. Uncons. Grave 11835.
Seaman NORMAN MACKENZIE
Last address in Lewis: 3 Portvoller
Service: Royal Naval Reserve, Patrol Service, HMS Lady Elsa
Service number: LT/JX 242662
Date of death: 1 September 1944 at the age of 38
Died in Addington Govt Hospital, Durban, of head injuries sustained on 27 August 1944.
Interred: Durban (Stellawood) Cemetery, Block F. Grave 458.