Hi John I can't help with the name variations, but the Islay marriages show John Dallas marrying Janet McGilvra on 3 Sept 1801 in Kilarrow (Bowmore) - both of this parish. John and Janet have 10 children from 1796 (really) to 1818. The mother's surname is shown as McGilvera, McGilvray and McGilveray. Janet is born in Mulindra in 1806. Looks like yours. Regards Seymour Hosking (Cameron/MacMillan/Kennedy/MacArthur.)