There are some WWII pillbox threads going on Facebook right now. Go to two Facebook pages: Coalhouse Fort Future and Medway urban explorer.I have the plans for the fort intended on Pelican Spit (basically nothing but a sandbar in the bay) until the CW began. They had done preliminary work such as warehouses, quarters for workers, the chief engineers home, and had begun sinking pilings before work stopped. I also have a sketch and description of the battery the Confederates built. In later years the spit became the Quarantine Station for immigrants coming into the port of Galveston. When they began dredging the Houston Ship Channel and Intercoastal Canal, the mud was dumped between the spit and a small island. Today Pelican Island is fairly large with a bridge connecting it to Galveston Island and what was the spit is now called Seawolf Park.
The pictures you posted look much like the main battery of Ft Crockett about 53rd St, just behind the Seawall. It was several hundred feet long with a covered gun emplacements on both ends. It cost too much to tear down, so they just built The San Luis Resort and Conference Center on top of it. The gun emplacement on the south end is still visible from the street today. Sorry to say, I do not have pictures of what they looked like back in my younger years.