Tom, Thanks for the picture of the expander. Because of the reflection in the picture, I can't see how long the threaded section is, but I assume it's pretty short, since a .223 case actually goes up into the tool head when the tool head is lowered all the way.
You said you purchased one of the first Super Star conversions. I'm thinking that Dillon must have changed the design of the powder slide housing and expander later on. I have a copy of one of his ads, and the powder slide housing looks like the one that I have. Unfortunately, due to the quality of the picture, I can't see what he is using for an expander. Your expander wouldn't work with my powder slide housing because I wouldn't be able to nut the expander from the top. Of course I could modify the housing that I have, but I hate to do that.