Hi Mamie
I don't know if I raise more questions than answers for you here. There is an Old Parish Register entry on Scotlands People for the marriage of a Joseph MacGown and Charlotte Sinclair on 19 July 1846 in Glasgow (no image available). There is also another OPR marriage entry on 10 April 1843 for Samuel McGown and Sophia Sinclair in Gorbals. There isn't an OPR entry for the birth of Samuel in 1846-50 to a Joseph/Charlotte.
The reason I've included Samuel above, other than he also married a Sinclair, is that when I searched the 1861 census in Stevenston, Ayr for all M*cgow*n, there were only 9 entries:
Joseph McGowan/ age 30/ collier/ born Ireland
Samuel McGowan/age 14/collier/ born Airdrie
Samuel McGown/age 37/collier/born Ireland
Sophia McGown/age38/born Inverness, Inverness-shire
Mary McGown/age 12/born Glasgow
Margaret McGown/age 4/born Stevenston, Ayr
Sophia McGown/age 0/born Stevenston, Ayr
Ann McGowan/age 78
Sarah McGown/age 77
I haven't viewed the entries for Ann/Sarah.
It might be that Joseph and Samuel were brothers, came over from Ireland together, were both colliers and could they possible have married sisters/close Sinclair relatives.
Sadly, with Charlotte's death probably before 1855 (I can't find one, like you, on SP) and also I can't find likely death entries in Scotland for Joseph/Samuel /Sophia, it's hard to confirm anything.
It's frustrating isn't it!
Regards.
Monica
PS: Falkyrn's find of a Joseph age 20 in the 1851 index could be Samuel's father. If Charlotte died around the time of Samuel's birth or shortly after, Joseph was very young (born around 1830, married around age 16 in 1846) - I wonder if somebody looked after Samuel in his early years until Joseph was in a position to look after him himself, which he did by 1861?