Get a newer Engine. While some engines require collapsed and closed meshes, there are plenty others that accept open geometry. Either way, with the amount of bad triangle stripping you have in your mesh, it wouldn't light well in the Old Unreal either. Even on that note, you wouldn't want to bring an object of this size…
I don't recall exactly where I saw it... but there was an environment artist from Epic who detailed how they constructed the architecture modularly in Gears of War. If you want to make environments, modularity is almost always your friend. Regarding your spec and normal maps: Specularity is never truly just black to white.…