I have a 75 gallon that I drilled myself. It was SO much easier than I expected it to be. Also, the bottom glass on all aquariums is tempered I believe.
If you want to test if your walls are tempered, you can take a laptop and open up notepad, make your screen as bright as it can get and set it on the floor of the tank. Then take some polarized sunglasses and hold them about a foot in front of your face and turn them 45 degrees either way. If the your laptop screen goes black, you're good to drill. If it is striped then go ahead and get a shiphon overflow. To test what tempered glass looks like you can do the same for the bottom. If I was a betting man I'd say your sides are not tempered.
But back to drilling the tank. I did it and the only problem I have with it is the exterior plumbing (PVC) attached to the overflow box takes up a bit of space and requires the tank and stand to sit out from the wall. I drilled mine in the top corner, about 4-6 inches away from the top and sides is what I was told is about where you want to be.
Check out
http://www.glass-holes.com. They sell kits that include the diamond tipped hole saw, and the overflow box, etc. You could get by with the 700 gph on a 55 gallon tank. That's what I have on my 75, with a mag drive 7 pump as well.
http://www.aquariumadvice.com/forums/f14/tjm80s-75-gallon-build-thread-138715-2.html
That is a link to my build thread, and you can see my overflow box. I just used 1.5" PVC from the overflow down to the sump. As for the return plumbing I have replaced the PVC with vinyl tubing for less resistance. I decided to come over the top rather than drilling the tank a second time for the return plumbing. Pretty simple actually.
Let me know if you have any more questions!
