What I want to know is that is there any difference between those two controllers? If so, what are they? Are they completely interchangeable?
All help is appreciated!

If it is old enough, it has a very heavy metal back plate that is highly desirable. If you are doing bolt-mods, somebody will surely appreciate that plate.clickykeyboards wrote: See my link for reference on different model M controllers.
http://www.clickeykeyboards.com/model-m ... 1987-1999/