Most 55 gallon aquariums are built out of thinner tempered glass and are difficult if not impossible to drill so IMO your best bet would be the water bridge.
But to join the 2 tanks would actually be more difficult than the airbridge. Drilling big holes in the side of my tanks would make me nervous. THen the joins basically have to be removable so you can move the tanks in the future.
It all just seems to hard
At least with the airbridge, you can just lift it out in 2 seconds and have 2 seperate tanks again. No mods to the tanks. If it springs a leak, the water flows back into the tanks, not onto the floor.
I seen something like that on ebay somewhere like a year ago. The tube was a glass cylinder about 4" to 6" across. Had I the money in my pocket and been able to pick it up.......would have been mine.