Hi, looking at the census of 1880 in the US, John Welsh and his wife both claim to be born in Scotland yet in the 1900 census they both say Ireland. I could not find a marriage for them either in Scotland or Pennsylvania but they could have married in New York or whatever place they met before Pennsylvania.
A tree on Ancestry says born Kilbarchan and in 1881 was in England and was with the Royal Navy.That was the only info the tree had on him. I looked at this and it is possible but you'd have to go further to see if it is actually him. The problem really is the fact that John & Welsh are very common names and with Welsh depending on who was recording an event, it could be transcribed as Welsh/Welch/Walsh so it is very hard to determine who may be correct without tracing down each possible.
I did find the births of 3 children;
Agnes born 18 May 1846 Kilbarchan
William born 10 March 1849 Kilbarchan
Jean born 15 February 1853 Kilbarchan
*all born to William Welch-Sarah McArthur
1881 Scotland census:
John Welsh
age:30 born @ 1851 Barrhead,Renfrew
living Kilbarchan,Renfrew
lodger with Fergus family
occ:general labourer
*this may be your John. I know it says born Barrhead but there is no birth of a John Welsh in Barrhead to any parents between 1830-1854. Also, he may not have been the one to give the census info.
another interesting guy;
1891 Scotland census
Paisley,Renfrew
James Welsh
age:32 born @ 1859 Kilbarchan,Renfrew
occ:gardener assistant
Annie Welsh
age:28 born @ 1863
there are a couple of John's in the 1891 census which could be him-one is age 37 & married to Margaret and the other is John with wife Agnes and son Robert age 5.
I also found this:
John Welsh
naturalization indexes
living at 4 Bartlett Place, Boston
born in Scotland
on 18 Sept 1855
naturalized on 23 October 1885
There are so many John Welshs you will just have to follow them down to see if he is yours. Sorry that there isn't much more definite but I would make sure that he actually wasn't still in Scotland. Possibly in Paisley. Kim