Here's my advice flchevygrl.
You can't drill the 55 as all panels are tempered and not to mention you will quickly learn to hate the width of a 55 gallon tank. So I would sell it. Instead I would go with a 40 breeder. This will allow you to drill holes (side panels are not tempered) for a proper overflow (I suggest a herbie) and the dimensions are much more reef/hobbyist friendly. I have a 40 breeder that is brand new, still with the labels on it you could have for $50 (what I paid for it). A glass company could cut you 2 panes to have an internal coast to coast overflow. As far as you return goes, just go up and over the back of the tank.
Then I would use the 30 gallon tank as your sump. I would have a glass company cut 4 glass baffles and silicone them in place. 3 baffles would be for a bubble trap and the 4th would be to make a compartment for a remote deep sand bed. So basically you would have 3 compartments. 1 on an end for your drain, filter sock, skimmer and heater. 2 on the other end for the remote deep sand bed. 3 for your return pump. You can tee off the return pump to feed the rdsb. Or make a small manifold to feed other equipment like a carbon reactor and gfo reactor. Since your space will likely be limited in the stand you can simply put your auto top off reservoir directly above the rdsb. (You don't want any light hitting the rdsb anyway.) And have a simple gravity fed ATO with a float valve and a simple back up dry float switch on a relay to close a solenoid. This will mitigate and risk of a freshwater flood. If you plan on keeping hard corals you can mix kalk in the ATO to replenish calcium and maintain alkalinity.
With this setup I think you'll find aquascaping the reef will be easier and more athletically pleasing. You can incorporate a quality and safe overflow. The 30 gallon sump will increase water volume. Finally, the maintenance free remote deep sand bed will keep your nitrates at undetectable levels. For more information on that Google "Anthony Calfo Sand Bed in a Bucket." The beauty of the rdsb is it doesn't have the pitfalls that an in tank deep sand bed has but has all of the same benefits. Plus it doesn't have the cost, maintenance, safety issues and other problems that come with a refugium. Not to mention the rdsb will be converting nitrate into nitrogen gas for complete automatic removal from the system, unlike a macro algae refugium that only assimilates nitrates. If you're wanting the refugium to provide a safe place for pods to breed you can simply place a plastic pond filter tray or Tupperware in the return section and fill it with rock rubble. This will act more like a cryptic fuge.
That is what I would do. If you need advice or have questions let me know and I'd be glad to help.