there was a paper by W W Gill in 1941 that examined the old names for Mann - when discusing regions with cognate names he has:
In what is now Scotland there once lay between the lower Forth and the upper Clyde an extensive British territory, the boundary of which has been obliterated for more than a thousand years. Its inhabitants called it Manaw, the Gaels called it Manann ; Campus Manand, ‘ Plain of Man,’ was the Latin form. The first mention of it occurs in the chronicle of Tighernach in the 6th century. From it issued the migrating body of Britons known to history as the Sons of Cunedda, who, perhaps disturbed by Scotic invaders from Ireland, moved South in the 6th century and took possession of North Wales. In the 7th-century Ravenna Geography it is recognizable as ‘ Manavi.’ In the 9th century it sent out Merfyn Frych to rule over Anglesey.* The name of this Northern Manann has survived in a few places which lie within its former boundary.

There was a paper by George Broderick that had some North Welsh roots in family tree for Manx Kings