Many thanks for your input, Forfarian. I agree, it is likely that John Longmore was illegitimate. He was with his maternal grandparents in both the 1841 & 1851 Census, while his mum, Isabella, was working nearby as a farm servant in Cluneymore in 1841 then by 1851, she is living at Slackbuie crofts Boharm with her husband, James Taylor and family.
Thanks for the information re the Baptist denomination not being around in 1836 in Mortlach... I will not go down that pathway! I also tried to get onto libindx earlier and couldn't do so. Will check again later and see if I can locate the whereabouts of the Episcopalian registers. I did organise for a researcher to look at the Mortlach Kirk Session minutes some years ago ... as luck would have it, they are not extant for the year of 1836!
John Longmore married Lillias Grant Findlay in Grantown INV in 1853. The marriage entry from the registers state he is from the parish of Speymouth, Moray. When John & Lillias migrated to Australia in 1859, John stated that both his parents were living in Banffshire.
Of course, my real interest in locating John Longmore's birth entry is that it just might lead me to his father. At the moment, my Longmore line stops right at 1836!