Hellfire,
I used a dremil too but I cut from the front where brian cut from the back.
I also followed the line but left about 1/4" below where my final cut would be,
to get a "feel" for the metal and the way it cut with the dremil.
Thats my only suggestion, leave yourself a little room to "fine tune it".
Also be aware that IF you follow the line all the way down like I did,
you'll have to fab yourself up a rear bracket,
which either means welding it on (ruining the chrome finish), or JB welding it.
Now IF you're gonna paint it, like I was and did, then messing up the chrome is no big deal..
Just go for it..
good luck.