Re the surname of William's wife Ellen, I can only see one death for an Ellen (searching *el*en to pick up on variants) near Williams birth year +/- 10 yrs:
1978 Alice Helen GOURDIE/ STRACHAN, age 84, in GLENROTHES, FIFE
With that first name of Alice, might explain why you have not been able to find the marriage:
1918 William Gourdie and Alice E Kennedy STRACHAN in BELLSHILL , LANARK
Monica