Aloha,
I may be the crazy guy who removed the top frame from one (and now another) 40 gal breeder tank, but IMO, I'm not so crazy when I say that cutting/drilling the thin glass on small tanks is too risky.
Regarding the coast to coast overflow, it has always seemed to me that it's too much for too little. The extension that requires a long length of silicone onto the back glass also increases the points of possible leaks later on. (A silicone seal on a painted glass surface is sure to fail.)
About full length vertical overflows, I have to say that they are a waste of tank space.
Some years ago, I concluded that overflow teeth get in the way. For some reason teeth have been made wider than the gap between them where the water is supposed to flow.
A flat spillway overflow requires less space and a lower water level at the spillway to achieve the same gph overflow. In place of the teeth, Bridal Veil Netting works awesome.

It's interesting to read all the different methods for getting
water out of a tank. Maybe I missed it but what about the "return"? How is
water to be returned to the tank?
Is the reason for the overflow
skimming action to keep a scum from forming on the surface? If so,
there are other options, some simpler than cutting into the glass and
creating increased risk of cracked glass/ruined tank.
Is the
point of these overflows to keep ugly plumbing and wasted space to a
minimum, If so, there are other options to consider. There is also a method of moving water within the tank which helps minimize scum.
Mahalo,
Mark

808-345-1049 call/text/visit anytime
Edited by Mark Peterson - December 12 2013 at 12:29pm