Regarding my post #14, I have been able to get a large resolution picture of each document on my camera, so if you pm me an email address, I can send them.
After trawling around every site, I agree that this George was (probably) the one born 1856 to Andrew/Harriet.
When George married, whether his birth was Nov (per baptism) or Dec. (per death reg), he hadn't had his birthday yet that year, so he would have been born 1856. He also says he was born in Kincardine, and it is highly possible that his mother had him at a sister/relatives home, but they actually lived in Aberdeen. That could be a detail his children were not aware of when they filled out forms regarding him.
As for the Harriet/Elizabeth problem: If you search Scotland's people for every McDonald in Duriss, (Duriss being the only consistent thing about her on the censuses; her age is not too consistent!), there is no Harriet, but there is an Elizabeth, born 1818. 1818 is pretty much in the middle of all the ages the censuses say. She could have been baptised as Elizabeth, but went her whole life as Harriet. Perhaps her parents "renamed" her after baptism, which is not unheard of.
MCDONALD
ELIZABETH
WILLIAM MCDONALD/ELSPET MCGREGOR
23/11/1818
256/10 188
Durris
George had older brothers; maybe track them down for descendants for DNA, if that is what you are after? Some of them appear to have vanished, but brother Alexander is not too hard to track.