I just saw "How Do They Do It" Season 11, Episode 20 on TV. They did a story on the Stanley Ferry Workshop. Here's a video that shows their moving bed mortiser.
https://www.youtube.com/watch?v=tD5wtd36NHc
The "How Do They Do It" story showed them planing huge timbers on a beautiful moving bed planer. The bed is as long as the stock and travels past the planer head to flatten and straighten rough timbers.
This is a moving bed planer at another canal lock workshop: