Well, adding those 3 lines to the very top of the ‘scene’ file I was importing did the trick.
I basically just had to stop trying last night because I was tired, and was getting all kinds of weird results trying to do what you said(like having the scene come up in a separate window, lol).
So I started again fresh today, made sure I was trying everything with new files, and it loaded the scene into the current window like I wanted. Although I didn’t notice much of a slow down with all the modules being loaded. Only thing I’ve noticed is that the scene I’m loading has had some funky effects on the camera (I’m using the most recent for of this FPS setup ) But I think I can work it out.
Thanks a lot for the help. 
As for that newish Level Editor, I had a problem getting it started. Posted in that thread about it.