From my recollections, they simply welded a piece of steel over the intake box, and occasionally removed the fan, with that being plated over, as well. I used to make it a point, to look inside one, when I had one, to see what was left. Never saw one "boarded up", with the brakes still inside. I would sometimes try to scrape/peel away blue paint, to uncover Red, but this was just to kill some time. Conrail did a massive switcher rebuilding, where they added a 26 schedule brake system, and standardized the controllers, and electrical system, to ease maintainance, I guess. I wouldn't mind having half a dozen Pups today, as a matter of fact..........