Not too likely it's a Mitsu fossil. Mitsu prefers a V-6 instead of the inline layout, which to me is a poorer choice as a straight 6 has a potential for a much stronger bottom end assy than a V design can match. The only justification for a V-6 design is that it can be shorter overall than a staight 6 can be.

And ... as odd as it seems although Mitsu always built their flagship model sports cars over the years with V-6s of 50% larger displacement than their hot rod 4-bangers they've never once taken top honors at the yearly DSM drag race shoot out held in Ohio

My best guess (and it's only a guess) would be it's either a Nissan or a Toyota as both manufacturers use a straight 6 design.