My Single Six is a 3-screw. I was looking for a steel ejector housing to replace the alloy housing that came on it. They used to be easily available. But, I did a number of searches on the web and found nothing for the old 3-screw models. I don't think the new model ones will fit, will they?
The housings went through several changes between late '53 and '63.
The housings offered by Ruger come in two lengths. Standard, which will fit most Rugers made and Long, which is designed for the long barreled Supers and the Maxi's. These housings will not work on barrels with the "stud" unless the housing is modified slightly.
So, if you want to upgrade your Single-Six to a steel housing and aren't trying to "restore" a gun then the currently offered housing should do the trick.