The deck plate on my 95' Striper 2150 broke and I cannot find a replacement with the 8" cutout size. I'm afraid to enlarge the hole because I don't know how to seal the decking to prevent water damage.
Here's one with an 8-1/2" in cutout: http://www.beckson.com/screwout.html
To seal the deck after enlarging the hole, use a dremel tool, or simply a use a gouge or chisel to remove about 1/2 inch of the core material between the layers of glass. Then fill the resulting void wit putty made from epoxy resin and cabosil.
If the deck is solid glass, not cored, you don't need to do this procedure.
Don't forget to seal the deck plate ring