We replaced a feedwater heater in the plant I used to work at. We used a heavy lifting firm whose primary business was removing diesel engines from ships to remove the old heater out and the new heater in. They had a modular skidding arrangement that pinned together to form a track. Each rail of the track had cross pins and they had a hydraulic apparatus that was fastened to the heater. The hydraulics engaged the cross pins in the track and literally pulled the heater along the track. Looked like a small railroad. In talking to the foreman what they typically did in ships was have an access hole cut in the side, they'd assemble the track, and then skid the engine(s) sideways out of the ship. I looked for some pictures of the setup but I must have lost them over the years.