While I get the whole tradition of sons taking mothers maiden name as a first name normally the Mc/Mac was dropped.
McGregor became Gregor
McDonald became Donald
Richardson became Richard
Ferguson became Fergus
Other names Stewart, Graham, Mitchell, Fraser kept the exact form
McLean never heard of a Lean and no I would never consider it.
For the poster who thought there was a difference between Mc/Mac they are both son of. Gaelic also has Nic which is daughter off but I've never seen it used outwith Gealic circles / BBC Alba. And I believe most girls are given Mc/Mac on their birth certificates even within the Gealic speaking communities.