Hi Sue,
I looked up the Aberdeen marriage: both are widowers in their early 30s. 'Wood' turns out to be first married name, not maiden. John McDonald is a steet porter not an engine fitter and he can't read and write ('X' mark for signiture) I could be wrong but it seems it would have taken some skill and some reading to be an engine fitter. I still have some credits trying to find john McDonald's death in glasgow between 1884-1891 but there are so many and I'm sorta guessing. I could also go backwards with Elizabeth's parents, Jane Lindsay and William Wood. I was hoping to find something on him since he was merchant seaman (I have another ancestor whi died at sea and found that record - funny enough another 'McDonald' but not the same branch)
Colin