Notching rear window for rollbar brace brackets

[LittleJon]

I've measured the amount of material to remove from the aft end of the rear window where it touched the 2 rollbar brace brackets under the turtle skin. It is a little more than an 1/8". What tool should I use to make the 2 notches? I was thinking a Dremel with a cutoff wheel, file or sandpaper around a pencil. This is the first time I am modifying Plexi.
Any help appreciated.