Factory sleepers are back in with most manufacturers these days, so it is not unusual to see extended cabs, and of course there are four-door crew cabs. However non-sleeper cab extensions are pretty rare, except in fire apparatus.
On June 2, 1990 I was passing the Commercial Safety College in Belmont NS, near Truro, and had the presence of mind to take the following series of photos.
In these trucks, cab extensions were built to accommodate student drivers and instructors. CSC had a wide variety of trucks, no two the same, presumably to give students experience on a variety of engines, transmissions and makes of trucks.
1. Ford Louisville tractor.