I have three of these and it seems a shame to run out and try to get a straight-sided Sankey keg. 'Hoff-Stevens' is really the tap name, we always called it a 'prong' tap. We called Sankeys 'ball' taps.
It is the 2nd from the left in this photo:
I'd have to patch the bung hole in the side, but otherwise I don't see how it's too different from the new ones. I'm leaning towards heating it with an open water bath that has electric elements in it.