Yeah, they were refurbished early in the privatisation era by Northern Spirit (though Arriva may have taken over by the time the fleet was completed). This included first class accommodation, still in 2+2 arrangement but with even more extra padding in the seats than the rest of the unit got. In my opinion this was the best the 158 got, with the 159s under SWT a close second.
When the Northern/TPE split happened and the 185s were introduced, the 158s were distributed far and wide. Besides the centre cars with Northern (which themselves had spells with other operators before returning north), I don't think any examples of this refurbishment remain:- but please correct me if I'm wrong.