Here's what I wrote back to davelin's PM:
Well, you know how that hood is made with the "flap" for access to the filter? I'm going to try and cut backwards from that opening (removing the flap) in the top towards the back side to make clearance for either a simple overflow or additional filtration. So it would be straight cuts, nothing fancy.
The standard filter/light system on the 6 gallon is useless for a nano, IMO so I need to DYI something else but I like the clean finished look of the top. If I ruin it, it's no biggie as I'll go with eggcrate, etc and just not have the top at all.
Thanks for your help, and as far as my name, I was a police K9 handler for years and am now on the dark side in the evil civilian legal field.