Well, having all four sides viewable on an undrilled tank is not something that I would want to try myself. Obviously, at least on of the side is going to have to have tubing, cords, etc, running on it, plus you will need a way to get power to the tank. Are you going to try and put equipment under the stand or do you have a remote sump?
I do not like over-flows myself because of the risk of a siphon break causing a catastrophic an over-flow. A lot of people still use them, but there are also a lot of folks that used to use them and don't anymore.
Personally, I would try to either
a) get the tank drilled or
b) skip the sump and use a hang-on or in-tank skimmer
If you are committed to using the tank as-is then I would recommend looking at one of the older tunze DOC in-tank protein skimmer set-up. The skimmer actually sits at the top of the water line inside the tank and seems to work pretty well. They make a model that is rated for a 250 gallon plus tank and it sells for $360 on MarineDepot.com.
Normally the in-tank skimmer is less than ideal visually, but in this case it would be less of an eye-sore than having the over-flow, drains, and returns running down a viewable wall on the tank IMHO. Add in a couple of Tunze streams for current and the only exposed equipment outside the tank would be power cords and possibly a very small top-off line. Of course, you will have to have power heads, heaters, and the skimmer in the tank. LIfe is full of compromises.
Jason