Upper Levels Upper level help

I've been through the photo galleries to find what I am looking for but don't see it, so I will ask. I am about to foster some pigs from the local rescue. They have brought in 30 pigs in the last month or so and have 5 pregnant females coming soon, so they need foster homes. My cage already takes up an entire room, so the only way I can add a cage is to go up. I currently have a 4x4 and a 2x4 connected by a little bridge. I was planning on putting another 2x4 above the 2x4 I have now. The 2 cages will be separated by a 1 grid "layer" on 3 of the 4 sides, to make cleaning my current 2x4 possible. I hope this makes sense. The side I plan to leave open (no grid layer) will be a 4 grid side. Does anyone else have this sort of configuration, and if so, will the upper level be stable? I use connectors instead of zip ties, if that matters.