You can use a belt sander to easily shape / even out the edge, etc.
Have you considered using something like 3M VHB tape, as an adhesive, instaed of drilling / using screws / bolts that will leak later. Also use something like Dow Corning 795 or 791 adhesive sealant to keep the water out.
I redid my deadlights using this method "sexy windows" thread on link below.
Very happy with it. They use the 3M tape to hold big windows in skycrapers, etc.
My old frames were through bolted to the cabin, but the acrlyic was just siliconed to the outside of the frame!!! So, now I have the acrylic sealed to the cabin, with no frame, no holes to leak. I tapered the black Dow 795 sealant along the edges, to give it about a 45 degree taper.
Was not able to upload pics here!!
Dscn0808 - Cruisers & Sailing Photo Gallery
new "sexy" windows - Cruisers & Sailing Forums
HOW TO HAVE SEXY WINDOWS!? - Cruisers & Sailing Forums