I like the thinking, but...
I don't see Mack being available @ 42. I like Unger more anyway, so I hope he'd be targeted (and available) @ 42.
Loadholt is truly a load, but he's got issues, such as his inability to play w/ good knee bend, does not have the quickest of feet, and has a tendency to jump offsides a bit (think of a much larger version of Rams OT Alex Barron, who has led the league in penalties). I'd pass on him 'til the later rounds.