I have just tried this, and it works perfectly, except for one thing: before this, when I was in the bare metal Slackware, I was able to open a second virtual terminal and start X with a different window manager on a second display. For example,
Ctrl+Alt+F2 for a second VT
xinit /usr/bin/fvwm -- :1
Ctrl+Alt+F8 to go to X on :1
Now I think I have one too many virtual consoles, and I am not able to do that. Is it enough to to comment out one of the entries in inittab and the corresponding entry in securetty?