You're most welcome, Ragna!

In my experience, it's tough when people were hiding something; they usually covered their tracks fairly well. Also, if people didn't have much money, that can make it less likely that we'll find documentation on them.
Maybe the local church would have a record of his burial. It all depends on what information the priest or minister recorded and what the informant knew. It's always worth a try, however, because you never know what you might find.
My great-grandfather's death record (in Canada) is useless. The information is either missing or incorrect (his mother's name is wrong). We know it's the same guy because we have his death notice and burial card. So the informant on the death record probably wasn't his wife.
It's possible that your great-grandfather might have changed his religion and his name and it's something to keep in mind. The key, at this point, would be in finding out where he was born because then you could search the census and birth records with a bit more certainty.
Much to my surprise, I found a Jewish ancestor (Barnett Barnett) who was born around 1796. His daughter (my ancestor) married in the Anglican church and her children were baptized in the Anglican church. Another daughter married a Jewish man and their children were raised Jewish. Most of Barnett Barnett's children married in the Anglican church. I recently learned that, despite being married in the Anglican church and baptizing his children in the Anglican church, his son, Benjamin, must have stayed Jewish because he is buried in the synagogue cemetery. So, who knows?
My mother's grandmother had to have known that her grandfather and some aunts, uncles and cousins were Jewish, but as far as I know, she never told her children about it. My mother and her siblings didn't know.
Hmmmm. You could see if the church where your great-grandparents were married has a baptism for him as an adult, in the year or so prior to their marriage.
I looked for a baptism for my 3rd-great-grandmother (whose father was Jewish but whose mother seems to have been Anglican) but couldn't find one. However, one of her sisters was baptized in the Anglican church when she was about 53 years old. That was a chance find; I was just trolling through the records.
I wonder about the way McLaven might have been pronounced and the various spellings that might have created? For example, I think Coughlin is pronounced "Cocklin" or "Coglin". Would Soundex pick up on Coughlin = Cocklin?
Someone recently told me that his ancestor changed the beginning of his name from Mac to Mc when he came to Canada but the reasoning seemed funny to me (I can't remember what it was).
I wish it were possible to search on surnames on Ancestry with a wildcard at the beginning of the name (for example, *ven).
Regards,
Josephine