From 'The Surnames of Scotland' by Dr. G.F. Black
McNarland is not listed, but see:
Early examples: James M'Nellane, servant in St. Ninians, Stirlingshire
John Maknellen, burgess and guid brother of Stirling, 1560
Other spellings: M'Knellane, Macknellan, McNilland
From Irish Mac an Fhirleighinn = son of the lector, or man of reading.
Firleighghinn or Ferleighinn was the title of the head of a monastic school,
e.e Ferleighinn Dubside in Iona, 1164. Also latinised as Virolecus.
Morice Macinnirlegin got excommunicated.
Dominic Macnafirlegind was accused of being a notorious fornicator in 1443.
Possibly also MacNair - several possible derivations, and many examples are given.
The MacNairs of Lennox are reckoned to be a sept of Clan Macfarlane. Maybe some of that family confused the spellings of the two names at some point ?